摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. The Fnraday Society i s not responsible for opinions expressed before it by Authors OY Speakers. mansactione OF FOUNDED 1903. T O PROMOTE THE STUDY OF ELECTROCHEMISTRY, ELECTROMETALLURQY, CHEMICAL PHYSICS, METALLOGRAPHY, AND KINDRED SUBJECTS. VOL. XXI. FEBRUAKY, 1926. PART 3. PHOTOCHEMICAL REACTIONS IN LIQUIDS AND GASES. A GENERAL DISCUSSION A GENERAL DISCUSSION on '( PHOTOCHEMICAL REACTIONS IN LIQUIDS AND GASES " was held by The Faraday Society on Thursday, October Ist, and Friday, October and, 1925, in the Lecture Room of the Sir Leoline Jenkins Laboratory, Jesus College, Oxford. THE PRESIDENT OF THE SOCIETY, PROFESSOR F.G. DONNAN, C.B.E., Ph.D., F.R.S., was in the Chair throughout the proceedings. The subject was considered under two main headings :- introduced by PROFESSOR A. J. ALLMAND. PART I. -" Einstein's Law of Photochemical Equivalence," (Thursday, October 1st) from 3 . 3 0 to 5 p.m. and 5.30 to 7.30p.m.) PART II.-" The Mechanism of Photochemical Reaction,'F introduced by PROFESSOR MAX BODENSTEIN. (Friday, October 2nd, from 10 a.m. to I p.m. and 2.30 to 5 9.m.) The President, in opening the proceedings, expressed the great pleasure and satisfaction feit by himself and all members of the Faraday Society that so many distinguished foreign men of science had found it possible to accept the invitation of the Society and were present that afternoon.Their presence was a happy augury for the future. He desired to extend a most hearty welcome to Professors Bodenstein, Christiansen, Franck, von Halban, Kautsky, Noyes, Ornstein, Stern, Weigert and Winther, and to Dr. Burger. The President then called on Professor Allmand to deliver his Introductory Address to Part I. 437 29 The Fnraday Society i s not responsible for opinions expressed before it by Authors OY Speakers. mansactione OF FOUNDED 1903. T O PROMOTE THE STUDY OF ELECTROCHEMISTRY, ELECTROMETALLURQY, CHEMICAL PHYSICS, METALLOGRAPHY, AND KINDRED SUBJECTS. VOL. XXI. FEBRUAKY, 1926. PART 3. PHOTOCHEMICAL REACTIONS IN LIQUIDS AND GASES. A GENERAL DISCUSSION A GENERAL DISCUSSION on '( PHOTOCHEMICAL REACTIONS IN LIQUIDS AND GASES " was held by The Faraday Society on Thursday, October Ist, and Friday, October and, 1925, in the Lecture Room of the Sir Leoline Jenkins Laboratory, Jesus College, Oxford.THE PRESIDENT OF THE SOCIETY, PROFESSOR F. G. DONNAN, C.B.E., Ph.D., F.R.S., was in the Chair throughout the proceedings. The subject was considered under two main headings :- introduced by PROFESSOR A. J. ALLMAND. PART I. -" Einstein's Law of Photochemical Equivalence," (Thursday, October 1st) from 3 . 3 0 to 5 p.m. and 5.30 to 7.30p.m.) PART II.-" The Mechanism of Photochemical Reaction,'F introduced by PROFESSOR MAX BODENSTEIN. (Friday, October 2nd, from 10 a.m. to I p.m. and 2.30 to 5 9.m.) The President, in opening the proceedings, expressed the great pleasure and satisfaction feit by himself and all members of the Faraday Society that so many distinguished foreign men of science had found it possible to accept the invitation of the Society and were present that afternoon. Their presence was a happy augury for the future. He desired to extend a most hearty welcome to Professors Bodenstein, Christiansen, Franck, von Halban, Kautsky, Noyes, Ornstein, Stern, Weigert and Winther, and to Dr. Burger. The President then called on Professor Allmand to deliver his Introductory Address to Part I. 437 29

ISSN:0014-7672    

DOI:10.1039/TF9262100437

出版商:RSC    

年代:1926

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No.13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions.Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. PART I.-EINSTEIN’S LAW OF PHOTOCHEMICAL EQUIVALENCE. INTRODUCTORY ADDRESS TO PART I. BY PROFESSOR A. J. ALLMAND (KING’S COLLEGE, LONDON) Received September 3 ~ d , I g 2 5 , I. Introductory. The application of the quantum theory to photochemistry dates in practice from the enunciation by Einstein in 191 2 of the so-called ‘‘ photo- chemical equivalent law,” a law which, stated in its baldest terms, says that, in a photochemical reaction, one quantum of active light is absorbed per molecule of absorbing and reacting substance which disappears.This simple and attractive relation, put forward with the authority of Einstein, has proved a great stimulus to research in a somewhat neglected field of chemistry, and a field, moreover, in which an impasse seemed to have been reached in respect of such matters as the primary mechanism of photo- chemical change, the significance of the part played by the absorbed light, and the whole question of the classification of photochemical reactions. I n this sense then, the relation has proved itself a working hypothesis of great value. To what extent it can be regarded as a (‘ law ” will be dis- cussed in the course of this paper. Before dealing with Einstein’s work, the writer would wish to emphasise particularly the degree of priority which is due in this field to Stark.This author published, four years previously to Einstein, two papers * which deal, in part, with the mechanism of photochemical change. In them are to be found, sometimes explicitly stated, sometimes only to be inferred, not only the photochemical equivalent relation, but also a clear distinction between the primary and secondary stages of a direct photochemical change, and an equally clear distinction between the mechanism of direct and indzrect (in- cluding semitised) reactions. Stark’s views undoubtedly did not receive from photochemists the attention they deserved-possibly because, as in- dicated, they were put forward more or less incidentally in the course of papers dealing mainly with other subjects ; possibly because they were clothed in qualitative language, and not given the dignity of a thermodyna- mical deduction ; perhaps because certain others of Stark’s views, with which they were bound up, immediately afterwards lost interest, in conse- quence of the development of new ideas on atomic and molecular structure by Bohr, G.N. Lewis, Kossel, and others. Whatever the cause, this neglect of Stark’s work has led to much misunderstanding as to the relations which 1 Pltysikal. Zcitsch., 9, 889, 894 (1908). See also Prinzipietz der Afom-Dynamik, II., 207 (1911). 43 8PROFESSOR A. J. ALLMAND 43 9 can exist between the number of quanta absorbed in a photochemical re- action, and the final chemical effect.11. Einstein’s Work. In dealing with Einstein’s work on this subject, we will distinguish be- tween his thermodynamic “proof” of the law, and his subsequent quite different deduction ’’ of the same relation.’ The thermodynamic proof appeared first in the form of two German papers,2 and then, during the following year, with a slightly different treatment, as a single French paper.3 In this proof a gaseous reaction of the type- XY + t - L X + Y, is considered. The dissociation takes place as a necessary consequence of and soZe4 by the absorption per molecule of XY of a m a n quantity t of radiant energy of frequency v-the recombination of X and Y takes place sole& with the simultaneous liberation of a m a n value of E units of radiant energy of frequency Y per molecule of XY formed.The reaction is thus a completely reversible one. The rate of decomposition of XY is assumed to be proportional to [XU] and to the radiation density (p) of fre- quency V. I t is assumed to be independent of [XI and of PI. The pro- portionality factor (A) entering into the rate of decomposition can depend on the temperature of the system (T), but on nothing else. The recom- bination of X and Y (and hence the liberation of radiant energy of frequency V) is assumed to take place according to the ordinary mass-action law, the velocity constant (A’) being dependent solely on temperature, and, in par- ticular, being independent of p. z, whether reckoned per molecule of XY formed or per molecule decomposed, is assumed to be independent of p.If now p is the black body radiation density for frequency v at tempera- ture T, then we are simply dealing with an ordinary thermal equilibrium. As a general case, however, Einstein imagines an equilibrium in which the radiation density p corresponds, not to T, but to T,, where T and T, are different (T, will be the higher in practice). Such a pseudo-thermodynamic equillibrium * is clearly only imaginable in a closed space, the walls of which are internally completely reflecting, and under such conditions is stable. Einstein considers a small virtual change from this pseudo-equilibrium state, equates to zero the sum of the entropy changes in the gas, the radia- tion and the constant temperature reservoir which surrounds the gaseous system, and arrives at a connection between p and T,, which, provided that the conditions are in other respects those under which Wien’s radiation law is valid, leads directly to the identity- t = h.(The Einstein Law.) I n the course of the proof, he shows that E, under such conditions, On the other hand, in the early part of the 1913 must be ind@endent ofT. The inverted commas are inserted by the writer to ernphasise the difference between the nature of Einstein’s treatment in the two cases-in the one, an exact mathematical proof of what will happen under the ideal conditions laid down, in the other practically a mere statement of what obviously will be the approximate result under another given set of conditions. Ann. der Physik. (iv.), 37, 832 ; 38, 8Sr (1912). your.de Phys., 3, 277 (1913). Einstein’s terms are ‘‘ aussergewohnliche thermodynamische Gleichgewicht ” and Such an equilibrium is not of course ‘‘ 6quilibre thermodynamique improprement dit.” to be confounded with the ordinary ’‘ stationary state ” of the photochemist.440 EINSTEIN PHOTOCHEMICAL EQUIVALENT LA\V paper, he states that c may be dependent on T. (It should again be emphasised that 6 is the mean energy absorption per molecule decomposed.) Later, assuming, as happens in practice, that a whole range of frequencies is active in causing decomposition, and that the total decomposition is the sum of those caused by the single elementary frequencies, he shows that I / , in the above formula, is the frequency of the radiation, and has nothing to do necessarily with any characteristic frequency within the molecule.Finally, it may be noted that, although deduced for a particular type of truly monomolecular gas reaction, Einstein expressly states that the result is a general one, and can be extended to more complex gas reactions or to reactions taking place in dilute solution. I t is unfortunate, that in none of his papers does he deal with these more complex cases. The result has been, inevitably, to suggest that the photochemical equivalent relation is more applicable to dissociations of the XY + X + Y type than to other kinds of reaction; whereas a consideration of reactions of the second order would have made more clear the fact that the relation strictly applies to the formation of the primary product of photochemical change, whatever may happen subsequently.This last point was first emphasised by Stark when putting forward a claim for priority in respect of the actual relation- Energy absorbed = NE = Nh,,, per mol and is, of course, of fundamental importance when dealing with attempted experimental verifications of the law. Einstein’s deductim of the photochemical equivalent relation follows quite different lines. The absorbing (and reacting) molecule is regarded as a kind of generalised Bohr model, capable of existence only in a definite series of energy states (Bohr states), and passing from one state to another by absorption or emis ion of a quantum. H e considers two such states Z,, and Z,, of corresponding energy contents Em and En, where E,)E, and Em - E, = hv.After dealing with such a system in temperature equilibrium, lie takes the special case where T is such that p, the radiation density corresponding to frequency Y, is very low. Practicallyall the mole- cules will be in the 2, (lower) quantum state. He further assumes that a molecule in the 2, state, besides reverting to the 2, state with emission of hv, can also, andfar more rapid&, undergo a different change analogous to a unimolecular reaction-say Z,+W. Clearly then, in such a system insolated with radiation of frequency Y from a source at a temperature higher than T, one molecule in the 2, state will be formed per absorbed quantum, and admost add will react further to give W, which corresponds to the PracticaZ vadidity of the law. It is of special importance here to note that theprimary and secondary reactions are clearly distinguished, which was not previously the case, and that the primary product, for the formation of which the law implicitly holds, is a higher quantum state.The process considered is, therefore, in appearance at all events, very different from that discussed in the thermo- dynamic proof. 1 A m . der Physik. (iv.), 38, 467 (1912). See also ibidem, 38, 888 ; 39, 496 (1912). Verh. d. deut. Physikal. GLS., 18, 318 (1916).PROFESSOR A. J. ALLMAND 441 I I I. Warburg's Work. Amongst the experimental researches which deal with the photo- chemical equivalent, those of Warburg,' published between the years of I 9 I 2- I g 2 I, occupy a very special position. This investigator was already, previous to 1912, engaged on a study of the energetics of photochemical reactions and was, further, in direct touch with Einstein.His work, henceforward essentially directed towards the testing of the Einstein rela- tion, is distinguished, not only by its experimental skill and accuracy, but also by the great acumen exhibited in the interpretation of the results obtained. We further owe to him a nomenclature which derives naturally from the Einstein relation, and which will be briefly discussed. The funda- mental photochmical equivalent ( p ) is a magnitude based on the Stark- Einstein conception in its simplest form-i.e. on the assumption that a molecule absorbs a quantum and then decomposes. It is the num8e.r of gram-mols required f a r the absorption of one gram-calorie of radiant energy of frequency V, and consequent4 the number of p-am-mols primari4 decomposing per absorbed gram-caZorie.We have- 4.186 x 107 = ___ A mols * = Nhv 28470 (where X is expressed in microns, h is 6.554 x IO-~?, and N is 6.062 x 10~~). Corresponding top, the theoretical figure which is reached only when the Einstein law is implicitly obeyed, we have 4, the speczjfc photochmical f e c t or the efective photochemical equivalent. This has the same dimensions (mols per absorbed calorie), but is a purely experimental magnitude, ex- pressing the final results of an actual photochemical reaction, and therefore including the effects of all partial reactions, whether primary or secondary. The term e~ectjvep~otochemicaZ equivalent, when used, expresses the number of absorbing gram-molecules actual& decomposed per absorbed calorie, whilst the term spect$c photochmical e f e d may refer either to mols of absorbing reactant (disappeared) or of resultant (produced).The equivalent radiant energy (I&) clearly represents the theoretical energy absorption in calories per mol of absorbing substance which dis- appears, calculated on the basis of one quantum absorbed per molecule. Finally, the quantum eJiciency (7) represents the number of absorbing molecules which have reacted per absorbed quantum. I t is given by the ratio +/p9 where + refers to the absorbing reactant, not to the resultant, is therefore the ratio of the efective to the fundamental photochemical equivalent, and becomes equal to unity if the law holds.There is obviously an analogy between these magnitudes and those suggested by Faraday in connection with electrolytic decomposition. Thus, to the Faraday, which is 96,500 coulombs per gram equivalent, corresponds the equivalent radiant energy ( ~ / p ) ? which is 28,47o/A calories per absorbing gram-molecule. And whilst, in electrolysis, we have- Fractional Current equivalents produced Efficiency = 96500 coulombs passed Sitsb. Prezus. Akad. Wissett., 1912, 216 ; 19x3, 644 ; 1914, 872 ; 1916, 300, 1228; 1919, 960. Zeitsch. Elektrochem., 26, 54 (1920); 27, 133 (1921). '3 Fundamen a1 has been chosen as translation of indiziertes. :{ Valenz-strahlung. Giiteverhaltniss.442 EINSTEIN PHOTOCHEMICAL EQUIVALENT LAN’ we have, in photolysis- Quantum Efficiency = y = t+,@ - 28470 mols decomposed x calories absorbed -- The magnitude I/P is, of course, simply Nhv expressed in calories instead of ergs.Analogy strongly suggests that the name of a Wal-burg might very suitably be given it. This is not the place to go into the details of Warburg’s work, and in any case some of his numerical results will presently be quoted. It is interesting, however, to follow how his views evolved during the develop ment of his researches. His first work was done on NH3 decomposition. He tacitly assumed direct dissociation to be the primary effect produced by the absorption of radiant energy, the small values of + found being due to exothermic recombination of N and H atoms. His early work on ozonisation of oxygen confirmed the probability of the dissociation mechanism, as he found two molecules of O3 produced per absorbed quan tum, a result obviously easily explicable by the successive reactions- His work on deozonisation, however, yielded results of great complexity, which could not be completely explained except by assuming that a part of the decomposition was due to impact between “ nascent ” 0, molecules of high energy content and O3 molecules.When he came to test the effect of wave-length on the reaction O2 3 O,, he found that the Einstein relation broke down, y becoming less at linger wave-lengths. This of course corresponds to general experience in photochemistry, which teaches us that, in practice, it is the shorter wave-lengths which are the more active, whereas the photochemical equivalent law, for equal quantities of absorbed energy, states the contrary; He further drew attention to the point that, if the Einstein law is valid, and the decomposition of a molecule results from the absorption of a quantum, the amount of decomposition per calorie of absorbed radiant energy will increase with wave-length up to a point, and then suddenly become zero when I/” no longer exceeds q, the energy necessary for the decomposition of a gram molecule.This of course does not happen, and Warburg consequently suggested that absorbing molecules should no longer be regarded as identical kith decomposing molecules one should write$ = ___ .f(A,P) where and that, instead off = ___ f(A,P) represents the fraction of the absorbing molecules which decomposes (I? is gaseous pressure).Considering further the relations between p and I/? he concluded that whilst the primary reaction in the case of 0, +03 may still possibly be 0 , 3 2 0 , decomposition directly to N c 3H is impossible in the case of the NH, molecule. His work on the decomposition of HBr and HI gave him the best agreement with the Einstein relation hitherto recorded, by him or any other worker, and at this stage he tended to distinguish sharply between the primary reaction in cases where the absorbed quantum is sufficiently large to decompose the molecule, and cases where this is not so. The latter type of photochemical change cannot be made the subject of quantitative prediction, the primary result of the absorption of a quantum being merely the formation of an ‘‘ activated ” molecule, which will sub- sequently, as the result of molecular collision, bring about chemical x A 28470’ 28470PROFESSOR -4.J. ALLMANI) 443 change. Fruitless collisions between activated ” and ordinary molecules are assumed to occur. The mechanism of NH, decomposition and possibly of the ozonisation of oxygen is supposed to be of this nature. In a later paper he dealt with the photolysis of aqueous KN03 solu- tions. Very low quantum efficiencies were obtained, and he ascribed them to the fact that much of the absorbed radiant energy was degraded by solvent molecules during the process of $absorption, and before the real photochemical action could set in. The wide absorption bands shown by solutions were referred to as evidence of such ‘‘ damping.” The larger the quantum and the smaller q, the more likely is the law to be obeyed.When, however, the reciprocal transformations of aqueous inaleic and fumaric acid were studied (small value of q) very low values of y were still got. Up to the end of his work, Warburg still assumed that a molecule was bound to decompose as the result of absorbing a quantum greater in size than -, provided that none of the energy was lost during absorption by molecular impact or damping. N IV. Summary of Experimental Data. In the following summary of data (pp. 444-5), only those researches have been noticed in which determinations of absorbed energy were actually carried out at the time-estimated quantum efficiencies, even those in Bodenstein’s well-known I 9 I 3 paper, are excluded.For the sake of completeness, data on solid reactions are inserted, as also are data on sensitised reactions, although the Einstein relation cannot of course be applied in its ordinary form to the latter. Gaseous reactions are given first, solid reactions last. V. Discussion of Experimental Data. Cases iiz which the Eiltsfein Law Holds.-Included under this heading are all reactions in which the absorption of N quanta (a) within reasonable limits of error, causes the decomposition of a single gram-molecule; (b> causes the decomposition of less than one gram-molecule, the figure however extrapolating to unity for the first stages of the reaction; (c) causes the decomposition of a larger number of gram-molecules, the number being readily explicable on the basis of straightforward stoichio- metric secondary reactions; (d) brings about the formation of N “acti- vated ” molecules, which then react stoichiometrically.The reactions thus provisionally grouped together are (a) Gaseous- decomposition of HBr, HI and C1,O; ozonisation of 0, by zogpp; bromination of C6H,, ; sensitisation of ozone decomposition by C1, : (b) Liquid-decomposition of uranyl formate and oxalate, of C1,O and of C10,; hydrolysis of CH,Cl. COOH; oxidation of Fe” ions by iodine; chlorination of CC1,Br ; sensitisation of CC1,Br oxidation by means of Br2: (c) Solid-the three quoted in the table. I t is not proposed to discuss these reactionsin detail, as that would raise the subject of reaction mechanism in its widest aspect. I t may, however, be stated that examples of apparent agreement with the Einstein law in its strict sense (molecular decomposition following quantum absorption) are comparatively few, and in several cases are perhaps rather better explained by assuming primary444 EINSTEIN PHOTOCHEMICAL EQUIVALENT LAW Reaction. Gaseous.HBr decomposition. HI decomposition. 0, -> 0,. C&O decomposition. Br, + C,HI2. 0, + 0,. NH, decomposition. c1, + so,. CI2 + co. C1, + H,. Sen sitised Gascous. 0, + 0, [Cl,]. 0, 0, [Br,]. Liq u a d. Uranyl formate de- composition (in H,O] Uranyl oxalate decom position (in H,O) C10, decomposition C1,O decomposition (in CCl,). (in CCI,). Author and Date. Warburg, 1916. Warburg, 1918. Warburg, 1912-21. Bowen, 1923. Pusch, 1918. Noddack, 1921. Warburg, 1913. Warburg, 1911-12.Kuhn, 1923-24. Bonhoeffer, 1923. Bodenstein, 1922. Bonhoeffer, 1923. Bodenstein & Dux, 1913. Bon hoeffer, 19 23. ao. Hatt, 1918. Biichi, 1924. Buchi, 1924. Boll, 1913-14. Bowen, 1923. do. Quantum. Effici- ency, t.e. y. 2.1 - 2 3 f o r About I t o r 460 P.E.C. 470 t+* For 253 PP- 0.28 in 0, mix- 1-07 in N, mix- 1.7 in He mix- tures. tures. tures. 0.23 for 209 ,up. 0-45 for 202- 214 pp at 20' C. ; 3 at 500' C, 0.1 for 206.3 p~ at 20' C. About 2-3 for 420 up. For 436 1000-1500 wit1 ordinary or moist gases ; 10-150 with very dry gases 2700 for 420 ,up. About 0.5 x I O ~ for white light. About 2 mole- cules of 0, for 420 PP- About 31 mole- cules of 0, for 420 pp. 0.4 for 420 pp 0'7 1, 420 11 1'07 I , 420 9 , jo molecules of H2C,0, for 254 p,u- 0.74 - 0'92 for 445 PP.0-83-1'02 for 445 P,u- Remarks. Independent of P H B r be- tween 10-400 mm. At 47.5 atm. Louer values with 125 and 300 atm. At 47.5 and 125 atm. <I with 300 atm. Limiting values of y for dilute 0, '' solutions 'I. For strong '' solutions " in 0, and N,, y can amount to 3.5 and 2'6 respectively. It is also much greater in moist gases. Practically the same figure over a pNHn variation of 50 : I (N, + H, present). Pressure has no effect be- tween 5-900 mm. Excess of hydrogen nullifies effect of rise of temperature. y increases with increasing [Cl,]. Traces only of 0, present. Larger amounts retarded reaction and CO, formation took place. I per cent. O2 present. Ordinary moist gases - trace of 0% present. Practically independent of ditto. COJ Probably tn iiiimtr nt values of y.Reaction of zero order. Very dilute solutions-air present. Concentration variation 10 : I had RO effect.PROFESSOR A. J. ALLMAND 445 0.32 - 0.35 at 254 PP. 1 for 579 pp. 1360 for 230 pp. ~ Reaction. 27'5 for 405 pp. 25 for blue light. NCl, decomposition (in CCl,). KMnO, decomposition (in H,O). K,Co( C,O,), decom- position (in H,O). H 0 decomposition $n ,H,O). KN 0, decomposition (in H,O). Maleic Acid 3 Fu. mark Acid (in H,O), A c i d + Maleic Acid (in Decomposition of H20 solutions of ferric salts of organic acids Hydrolysis of chloro- platinic acids. Fumaric H2O)- H y d r o l y s i s o f CH,CI . COOH. H y d r o l y s i s o f CH,Br .. COOH. Fe" + I, (in H,O). Hydrolysis of Acetone, Cl, + zCBrC1, in CCl, and in SiCl, C1, + Toluene.I, -t- K,C,O,(in H,O), Sensifised Liquid. 0, + zCBrC1, (in CCI,) Maleic Ester + Fu- CBr& maric Ester (in CCl,) CBr2l. Solid. AgBr decomposition. o - nitrobenzaldehyde 9 o-nitrosobenzoic acid. Sensitised Solid. AgCl decomposition CAgl. Author and Date. do. Rideal and Norrish, Vranek, 1917. 1923. 3enri and Wurmser 1913. Kornfeld, 1921. Warburg, 1918. Warburg, 1919 do. Winther and Oxholt- Howe, 1914. Boll, 1914. hdberg, 1924. do. aideal and Williams Henri and Wurmser 1975. 1913. Ncddack, 1921. Griiss, 1923. Book and Eggert, Berthoud and Bel- 1923. lenot, 1924. Griiss, 1923. Eggert & Borinski, 1923. Eggert and Nod- dack, 1923. Bowen, Hartley, Scott and Watts 1924. Weigert, 1921. Quantum Effici- ency, Z.C. y. 5 for 238 pp changing con- tinuously to 0'004 for 546 PP.I molecule of 0, for 420 pp. 680 for 365 pp. 560 9 , 436 1 , 430 3 , 557 9 , 0.75-1.08. About I for violet light. I for 436 pp. Remarks. Practically independent of Concentration. Light between 214-298 pp -mean about 230 py. } Monochromatic light. Depends on concentration, acidity, etc. For N/3 KNO,. Smaller values with lower con- centrations. For 0.01 M. solutions. y increases at lower con- For 0.01 M. solutions. y decreases at lower con- centrations. Dependent on time, A, and concentration. Used 313-436 pp. Arbitrary concentration. y is less at lower concentra- tions. Thus, for 254pp, 4 at 2 x 10-7 mo1s.lc.c and 0.3 at 0'2 x 10'; moIs./c.r. centrations. Solutions far weaker than with CH,Cl. COOH. y became less than unity when [CBrCl,] became too low. At - 80" C.Independent of [O,]. Only slightly dependent on concentration. For 365, 406 and 436 yp. Became less as reaction proceeded. Became much less a s re- action proceeded.446 EINSTEIN PHOTOCHEMICAL EQUIVALEN‘T LAW formation of an L L activated ” molecule, which does not subsequently necessarily react stoichiometrically. That is, certain cases of agreement may simply be coincidences. Thus, Stern and Volmerl suggest this even in the case of HBr decom- position; the quantum corresponding to 209pp may not be big enough to dissociate an 0, molecule into atoms;, the data on C1,O decomposition as gas and in solution necessitate different secondary reactions in the two cases if decomposition to C1, and 0 is regarded as the primary reaction; although the sensitisation of O3 decomposition by C1, can be explained by a simple stoichiometric mechanism, this is not the case with the same reaction sensitised by Br,; if the low value of y for CH,Br .COOH hydrolysis compared with the value for CH,Cl. COOH hydrolysis has anything to do with the low concentration employed in the former case, as seems possible, a simple stoichiometric mechanism cannot hold ; the chlorination of CC1,Br may very well be the result of the primary forma- tion of an activated chlorine molecule;* in the sensitisation of the oxidation of CC1,Br by means of bromine, the disappearance of one molecule of oxygen per absorbed quantum may well be a coincidence. The best support at present available for the view that the primary process in a photochemical change is molecular dissociation is perhaps contained in the papers of Bodenstein and Liitkeme~er,~ Berthoud and Bellenot,6 and Dhara7 Reactions with Low Quantum EBciencies.--But few have been actually measured.They include the decomposition of weak ‘‘ solutions ” of O3 in 0,, of NH, at low temperatures, of KNO, and KMnO, solutions; the hydrolysis of the chloro-platinic acids by light of long wave-length and of brom-acetic acid at the concentrations worked at by Rudberg; the trans- formations maleic acid Reactioits with Nigh Qziaiztum Eficie?zcies.-These are more numerous. In particular, as will be seen by reference to the tabular summary, many reactions involving the halogens, whether as reactant or as sensitiser, have high values of y. Other well-marked cases are the decomposition of aqueous solutions of H,O, and of organic acid ferric salts, the hydrolysis of acetone and the decomposition of dilute solutions of uranyl oxalate in presence of air by 254pp. Efect of Wave-Length.-According to the law, one should have one molecule decomposed per absorbed quantum, independently of the size of the quantum.This latter is directly proportional to the frequency of the light and inversely proportional to the wave-length. For a given energy absorption therefore, the number of molecules decomposed should be proportional to the wave-length, the quantitative relation being given by the equation- fumaric acid in aqueous solution. This requirement of the law is well fulfilled in the cases of the decom- position of gaseous HBr and HI, and, less accurately, in the case of the decomposition of solid AgBr.But these are the only instances investigated 1 Zeitscli. Wiss. Pliot., 19, 275 (1920). Warburg, loc. c i t . (1914, 1916, 1921). 3 Nernst and Noddack, S i t z b . Prezcss. Akad. Wiss., 1923, 110. 4Nernst and Noddack, lor. c r f . Zettsch. Plijlsikal. C h e w , 114, 208 (1924). Trans. CIitm. So:., 123, 18 56 (1923). ‘ H H E ~ v . Chim. A d a , 7, 307 (1924).PROFESSOR A. J. ALLMAND 44 7 in which y is independent of X No case is known in which y increases with A, if we omit the irregular changes shown in the maleic acid fumaric acid transformations investigated by Warburg. In fhe majarity of cases, y increases as X decreases, corresponding to the universal tendency towards increased photosensitivity at shorter wave-lengths.As y = +/p, and as p decreases when A decreases, a conconiitant decrease in 4 should take place, if y is to remain independent of A. I n certain reactions 4 is found to be independent of A-that is, the absorp- tion of a certain amount of radiant energy causes the same amount of chemical change, whatever the wave-length of the light. Such is said to be the case for example in the decomposition of H,O, solutions by short wave-length light,’ and in the transformation of maleic ester into fumaric ester when sensitised by bromine., In these circumstances, y increases with increasing frequency. Still more so is this true, whn + acfzcally in- cnases as A decreases, i.e., changes in the opposite sense to that demanded by the Einstein Law. This is the type of behaviour observed, for example, in the ozonisation of oxygen, the hydrolysis of the chloro-platinic acids, and the decomposition of aqueous solutions of KN03 and K,CO(C,O~)~ In respect fhrpfore of fh efect of wave-length, the Einstein law holds bad& in practice.E f e c t of Concentration of Absorbing Substance.-Omitting sensitised reactions, we find first of all a number of cases in which y is independent of concentration over a considerable range. Such are, for example, the photolysis of HBr, NH,, U02C204, K,Co(C,O,), and C10, (in CCI, solu- tion). In the reactions 02+ 0, and maleic acid+fumaric acid, y becomes lower as the concentration increases. Whilst in many cases, y increases as the concentration of the absorbing substance increases-eg., COC1, formation ; the decomposition of 0,, of H20, and of KNO, ; the hydrolysis of the chloro-platinic acids ; the transformation fumaric acid+ maleic acid.E@ct of Zmperature.-The only work on record is that of Kuhn3 dealing with the decomposition of ammonia gas. y increases with rising temperature. y then increases very rapidly with U. None of them shows a high value of y. VI. The Conditions of Validity of the Einstein Law.4 The above discussion will have made it amply clear that the ‘‘ law ” seldom holds when applied, as is usually done, in connection with the complete reaction. I t will be equally obvious, from what has been said, that the reason is very often the occurrence of one or more secondary reactions, the nature of which remains obscure. The subject of such secondary reactions is closely bound up with the subject of the mechan- ism of photochemical change and for that reason will not be considered here.Quite apart however from this, th quantum rehution should strictZy on& be ajpZied to theprimary reaction, a point, as we have seen, first made clear by Stark, and afterwards insisted on by Warburg. The question which then arises is-does the law hold for all primary photochemical reactions, and if not, for which ? Einstein’s ‘‘ deduction ” deals with one kind of primary Why is this? 1 Henri and Wurmser, C.R., 157, 126 (1913). 2 Eggert and Borinski, Physikal. Zeitsch., 24, 504 (1923). 3C.R., 178, 708 (1924). 4 Good recent papers dealing with the photochemical equivalent relation are those of Warburg, Zeitsch.Elektroch., 26, 54 (1920) ; Nernst and Noddack, loc cit. ; Weigert, Zeitsch. f a r Phjis., 14, 383 (1923).448 EINSTEIN PHOTOCHEMICAL EQUIVALENT LAW reaction only, the production of a higher Bohr state. Other kinds are presumably possible. So we will take for consideration Einstein’s thermo- dynamic proof. Not only is it more comprehensive in respect of possible primary reactions, but, as has already been hinted, much of the confusion which has arisen in connection with the interpretation of the law is due to the fact that no clear distinction is made in the proof between theprimary and the compZete reaction. The equation arrived at by Einstein is- where T, is the temperature of the radiation of frequency v and pTs the corre- e is the average quantity of radiation absorbed per molecule of XY reacting N and R have their usual significance ; a is an integration constant 1 and independent of temperature ; A’ is the velocity constant of the reverse reaction : sponding radiation density ; to give X + Y; x + Y+XY + € and is dependent on temperature on& ; A is the ordinary ‘‘ intensity formulation ” photochemical reaction velocity constant (the ‘‘ photochemical susceptibility ” of Boll and Henri) and is dependent on temperature only.As now pTs and T, are functionally connected in a way independent of the temperature of the system (T), and as, further, AT, is sufficiently small A a for Wen’s law to be obeyed, both - and c must be independent of T A under the conditions Zaid down 6y Einstein in his proof; whilst the relation E = hv follows directly.(As has been pointed out, Einstein states in one of his papers that E can depend on temperature, and seems conse- quently to be contemplating cases in which the law cannot strictly hold, even for the primary process.) That the law cannot be expected to hold in practice for a complete photochemical reaction in which Nr is identical with the total energy increase per gram-molecule transformed,z can easily be shown. For then, as a is independent of temperature, and as, according to Einstein, both A’a A A and A‘ are functions of temperature, if - is to be independent of dA and dA‘ must be identical. I n actual practice, x ’ n A”dT temperature, I this is very unlikely to happen. .,4’, being an ordinary chemical reaction velocity constant, will certainly vary with temperature more rapidly than A, A’ A [XI [Yl I For-consider the case in which T, =T.Then p = -a. c RT. But - ~ A A‘ - [X Y ] N E N € Q _ - RT = KT. Hence KT = ae Hence a = C and Q = Nc. and I ~ z K T = h a - KT. But ZUKT = - R~ f ZUC. See previous foot-note.PROFESSOR A. J. ALLMAND 449 a photochemical reaction velocity constant. There is no doubt however that, in the Einstein proof, Q is equal to Nr. We are therefore dealing with a type of process in which the complete reaction and the primary reaction are identical, a process in which represents equally the average total energy increase per molecule ultimately transformed and also the average energy of acfivatzon or criR’CaZ increment per molecule, a process moreover in which both E and - are independent of temperature.I t would seem then that Nhv or NE is fundamentalh the molar energy of activation involved in the primary photochemical process, and only under the particular conditions assumed by Einstein in his proof is it identical with the total energy change, and the primary process identical with the complete process. A’ A Let 4 be the gram molecular energy of activation for XY-x + Y, x + Y-XY. and q’ the same for Then, generally, we shall have and, in the present case, as Q = q, we have 4’ Hence the state X + Y is fundamentally state XY. Further, as E is independent of T, T, = r q - = 0. unstable with respect to the we can write (putting again where K = ApT, k’ = A’ and c and c’ are integration constants. We get at once that k‘ = 6’-that is, that A’ is independent of temperature.If, however, A‘ is independent of temperature, so must also be A, the photochemical reaction velocity constant. The causes which can affect the temperature coefficient of photochemical reactions are discussed in an im - portant paper by Tolman,l who deduces the equation- dink, : - z - = - aT kTL9 where 2 is the average energy before activation of all molecules which can pick up a quantum and react, E is the average energy of aZZ molecules, and K , is identical with our coefficient A. The fact then that A must be inde- pendent of T under the conditions assumed in the Einstein proof means that 2 and E are identical, and that all molecules must equally be in a posi- tion to react on absorption of a quantum.All molecules are therefore at the same energy level, no molecule requires preliminary activation before it can react as the result of absorbing a quantum, and the critical increments of the separate molecules are equal to one another. 1 your. Amer. Chem Sx., 45, 2285 (1923).4.50 EINSTEIN PHOTOCHEMICAL EQUIVALENT LAW Th &4e ofphotochmical change then for which t h Einstein thrmodyna- mic proof rZgidZy holds is one in which (a) all reacting molecules are at the same energy Zevel before reacting and are hence equally reactive ; (b) the re- activi9 of th absorbing molecules under a given radiation dens@ is inde- pendent of temperature ; (c) the amount of energy absorbed per absorbing mobcute is the same in every case and is independent of temperature; (d) the product after the absorption of energy is fundamenfa@ unstable with respect to the ortginal absorbing system, and will revert to th latter spontaneoudy at n rate independent of temperature.The whole process is identical for all the molecules. I t is interesting to note that these four conditions are all fulfilled by the change 2, + hv -3 Z,, the passage from a lower to a higher Bohr state which forms the primary reaction in the Einstein 1916 deduction, and it is clearly of importance to know whether other primary mechanisms which have been suggested in connection with photochemical reactions also fulfil these c0nditions.l Apart from such generalised terms as “ activation ” of the molecule or a rise of the same to the ‘( critical energy level ” (Perrin, W. C.Lewis, Winther, Weigert), following on the absorption of a quantum (by molecule, group, atom or electron), suggested mechanisms can be grouped as follows :- 1Mechanism. Limiting Case. ~ Actual loss of electron Loosening of valency electron Polarisation of molecule Wide separation of constitutents ~ Breaking of bonds or dissociation (Stark, Volmer, Bodenstein) (Winther, Bodenstein) (Baur) . negative ions (War b u r g ) Ionisation into positive and + (Einstein, Warburg, Nernst). I t would appear that the ideas here indicated are not sufficiently well- defined to enable them to be discussed satisfactorily from the present point of view, although it would certainly seem that the above conditions would not be fulfilled in the ‘‘ limiting cases ” referred to. Thus it might be ex- pected that a photochemical reaction in which the primary process were dissociation of a molecule would not obey the Einstein law, however simple any secondary reactions.Presumably also there is a connection between the rate of return of the activated product to its original state and its in- herent instability. I f consequently primary activated products were found with lives considerably longer than the I o - second characteristic of the higher Bohr state, one might anticipate that reactions in which these took part would not follow the Einstein law. Assuming, however, that an activated molecule does always have the properties of a higher quantum state and obeys stipulation (d), it may be of interest to discuss briefly why, even then, the Einstein relation may fail in practice when applied to the primary stage of a reaction.we get K Consider the equations on page I 2. Remembering that KT = at once that C = and hence that A’ = 5 C’ Remembering also2 that 1 Stern and Volmer (loc. c i t . ) , prefer to regard Bohr states as primary products in all cases. 2 P. 448.PROFESSOR A. J. ALLMAND 45 1 u = C , the basic Einstein equation becomes- where -4 and E must be independent of temperature if the law is to hold. I n practice, however, A does increase slightly with temperature, and some- times appreciably so. This is doubtless in part due to the fact that it is actually determined for the complete reaction, whereas the primary reaction is now under consideration. But we should hardly be justified in conclud- ing that the temperature variation is entirely due to secondary reactions. E represents the average molecular critical increment and this, in practice, one would expect to decrease with rise of temperature.In fact, as pTs and T, are functionally connected independently of temperature, A and E, if they vary with temperature, are bound to do so in opposite senses and to com- pensating degrees. Under such conditions, E and hv cannot be equated, even if Wien’s law holds, and hence the Equivalent Law can, at the best, only be approximately true. Clearly the approximation will be the closer, the smaller the degree of de- pendence of A and E on temperature. In a case where secondary reactions of a chemical nature have a negligible effect, a high temperature coefficient must mean ( I ) that E rapidly becomes less and y greater as the temperature rises (2) that the Einstein law will not be obeyed.A normal value of y at low temperatures becoming abnormally high with rise of temperature would suggest secondary reactions-in the present case one would rather expect an abnormally low value of y and a high temperature coefficient at low temperatures, y becoming normal and the temperature coefficient be- coming unity (dA/dT zero) at higher temperatures. The writer has compared existing data on y and on temperature coefficient, but the results are not il- luminating-the relations looked for, if they exist, are obscured by secondary reactions. Tolman’s work on the significance of photochemical temperature co- efficients has already been mentioned. Suppose that the absorbing substance can exist in three quantum states Zl, Z,, and Z,, of which Z1 is the lowest, and Z3 an ‘‘ activated ” state.The ordinary substance consists of a mixture of 2, and 2, molecules, the proportion of 2, increasing with temperature rise. A positive photochemical temperature coefficient means that partial activation is required before the full quota of activated molecules is formed in the light field. In principle, this can happen in two ways. ( I ) AZZ ab- sorbing moteczdes react, but molecules in the 2, state cannot absorb. A temperature rise, therefore, increases the number of absorbing molecules, reacting molecules and amount of absorbed energy-aZi in the same ratio. Hence, whilst A increases, c (or y) remains unchanged.This would corre- spond to an experimental case in which an increased rate of photochemical action at high temperatures was entirely due to increased absorption. (2) AZZ absorbing mokcuZes do not react, but only those in the 2, state, the number of which is increased on raising the temperature. A temperature rise therefore increases the number of reacting molecules but not the total amount of absorbed energy-2.e. A increases and e diminishes. This would appear to be the real practical case, for, so far as is known, increased ab- sorption usual.ly accounts for but little of the increased rate of reaction ob- served at higher temperatures. I t is also in agreement with the requirement, mentioned above, of simultaneous change of A and c with temperature. I t 1 P.448.452 EINSTEIN PHOTOCHEMICAL EQUIVALENT LAW further accounts for the well-known results of Padoal on the effect of 011 the temperiture coefficient of photochemical reactions, for the smaller the active quantum, the greater must clearly be 2, and hence also the tempera- ture-coefficien t. VII. General Conclusions. One may say then that, in practice, there are the following reasons why the Einstein relation generally does not hold. (I) The secondary reactions (not considered in this paper) are not coupled stoichiometrically with the primary reaction as assumed in the 1916 deduction. (2) The absorbing molecules are not all “activated ” as the result of absorption. This may be due (a) to the quantum being too small to raise the particular absorbing molecule to the critical energy level, in which case, as we have just seen, the yield of primary product will be affected by temperature or (b) to loss of energy by “damping” during absorption (Warburg), even although the quantum would be large enough if it could be completely u tilised. (3) Possibly the primary process may result in the formation of a pro- duct which is not essentially unstable with respect to the absorbing mole- cules, i.e., Q and q are not equal. (4) Again possibly, though not at all likely, the conditions may not be those of Wen’s law, or the product AT, may be too high. A simple calculation will show however that, for example, with radiation of wave- length 300 U P , T, may reach 2ooooo C. and Wen’s law still approximately hold. Under the conditions laid down in the 1916 deduction and implied in the 19 I z proof, the law is of course bound to hold, though it would seem also, from the fact that is the mean energy absorption per molecule and in one paper is referred to as being a function of temperature, that the author has had in mind “ practical ” cases of approximate validity. I f the “ deduction ’’ had preceded the thermodynamic proof in point of time, much misunderstanding of the relation would have been avoided. It was particularly unfortunate that a chemicul dissoczatioiz appeared in the proof both as primary and as complete photo-reaction. From the practical standpoint, owing to the far-reaching results of secondary reactions, we are left simply with the idea of absorption of light as quanta, after which very little can be said as to what will happen. But the introduction of the simple and definite quantum conception was in irself a great advance. I t clarified our ideas on the classification of photo- reactions, reconciled the conflicting (‘ intensity ” and “ absorption ” formula- tions of photochemical change, settled (at all events for the time being) the questions of threshold intensity and photochemical extinction, and thrust into the background speculations on the existence of photochemical, as distinct from thermal, absorption bands-all this quite apart from the valuable new ideas which followed in its train. And whatever the value of the ‘‘ photochemical equivalent law ” in itself, there is no doubt of its formu- lation by Einstein having been the most potent factor in securing due and rapid recognition by photochemists of the Quantum conception. University of L o d o n , King‘s College, August, I 9 2 5 . E g . , Linc. R ~ i t d i . , 25 (II.), 215 (1916).

ISSN:0014-7672    

DOI:10.1039/TF9262100438

出版商:RSC    

年代:1926

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. ON THE CONFIRMATION OF THE EINSTEIN LAW OF THE PHOTOCHEMICAL EQUIVALENCE I N A VERY SIMPLE PHOTOCHEMICAL REACTION. BY PROFESSOR DR. FRITZ WEIGERT AND DR. LOTTE BRODMAN’N (LEIPZIG). TRANSLATED BY A. LEWIS. Received&& 2 7th, I 9 2 5. The peculiar nature of the Einstein equivalence law is such that its confirmation by means of experiment must apply solely to the primary photochemical process. Now the result of the first change in the molecule. produced by the absorption of a quantum, is never identical with the chemically determined product at the end of the photochemical reaction.Moreover, the primary process is followed by various chemical, electrical or kinetic changes leading to the end product, about whose nature we can only make a conjecture by analogous processes in highly rarefied gases. Hence we may expect that a photochemical reaction, which from be- ginning to end takes place in the same molecule would show simple rela- tionships. Such reactions can be found in those organic isomeric changes brought about by light. The first research of that nature from the stand- point of the Einstein law was carried out by E. Warburg.l But this work on the photochemical change of maleic to fumaric acid and the reverse action, resulted in a value far too small for the quantum efficiency. E.Warburg has given a very simple form for the testing of the Einstein law 2 which we will now proceed to follow. The ‘‘ Photochemical Yield ” or the c L Effective Photochemical Equivalent ” 4, which specifies the number of gram molecules transformed per calorie of absorbed radiation, is de- termined experimentally. This is then compared with the ‘‘ Fundamental Photochemical Equivalent ” p , which on the basis of the Einstein law can be calculated from : X mole p = -- (A in p). 28540 cal The ratio (pip the “ Efficiency Ratio ” or ‘( Quantum Efficiency,” assuming the validity of the equivalence law, is equal to n or I, where n is a small whole number or unity. In the photochemical isomeric change of maleic and fumaric acid, the quantum efficiency was found to be much smaller than unity, and E.Warburg n 1 E. Warburg, Berliner Akad. Ber., 1919, 960. 2 E. Warburg, Zeitschr. fur Elektroch., 26, 54, 1921. 453 30454 CONFIRMATION OF EINSTEIN LA\\: explains it in this manner ; that following on the absorption of the quantum, the two parts of the molecule are torn asunder, and unite again in one or the other manner according to probability. The simple assumption men- tioned above that the whole change shall take place in the same molecule, is therefore not valid. On the other hand this appears to bp the case inanother reaction which was discovered by G. Ciamician and P. Silber,* and which was later sub- mitted to an exhaustive quantitative investigation by F. Weigert and L.Kummerer.2 This reaction is the change from o-nitrobenzaldehyde into o-nitrosobenzoic acid- We have now again taken up the investigation of this reaction from the standpoint of the Einstein law. o-Nitrobenzaldehyde was dissolved in acetone and mas insolated with the single colours of the quartz mercury lamp. The analytical determina- tion of the resultant o-nitrosobenzoic acid was made by conductivity measure- ments. In purifying the aldehyde and the solvent as well as in the analysis, we followed precisely the directions of the earlier workers. The filters for isolating the strong spectral groups of the mercury arc at 436, 405 and 366pp were somewhat different from the earlier ones.3 The energy measurements were carried out with the surface bolometer of Lummer and Kurlbaum using a compensation lead, as described by 0.Warburg and E. Negeleix~.~ The bolometer had an effective surface of 9 cm.2, and was standardised several times against the Hefner candle iliaking use of Gerlach's value. For the calculation of the photochemical yield, one must know what portion of the incident radiation, the whole of which was measured on the bolometer, is absorbed by the light sensitive portion of the system, that is the o-nitrobenzaldehyde. For that purpose were placed at our disposal the as yet unpublished measurements recently carried out by J. Hyman,6 following the very exact photo-electric method with two cells of H. von Halban and K. Siedentopf.' From these we find that the extinction co- efficient of a I per cent. solution of o-nitrobenzaldehyde, and o-nitroso- benzoic acid in pure acetone in a layer of I cm.thickness, is :- 436. 405. 36%. o-Ni trobenzaldehy de 0.0153 0.81 12'2 o-Nitrosobenzoic acid 0.1 30 0.6 2 13'7 The insolation vessels were simple troughs of plate glass, which are transparent even to the ultra-violet rays. 1 G. Ciamician and P. Silber, Bm. Dlsch. Chem. Ges., 35, 2040,1go1. a F. Weigert and L. Kummerer, Bey. Dtsch. Cliem. Ges., 46, 1207, 1913; 3 The experimental details will be published later. J 0. Warburg and E. Negelein, Zeitschr. f. Phys. Chem., 102, 255, 1922. 6 J. Hyman, Diss., Leipzig, 1924. 7 H. von Halban and K. Siedentopf, 2eitschr.f. PhysiR. Chem., 100, 208, 1922. L. Kummerer, Diss., Berlin, 1914. W. Gerlach, Phys. Z~itschr., 14, 577, 1913.DR.FRITZ WEIGERT AND DR. LOTTE BRODMANN 455 0. 15 I5 I5 I5 15 15 15 The percentage of the incident radiation absorbed was calculated from the extinctions given by Hyman for o-nitrobenzaldehyde, and inserted under A in Tables I.-111. TABLE I. H g 366, p = 1-31 . 10 - 5. (Symbols on the following page.) t. -___ h. m. 6 I5 6 I5 6 45 6 7 6 28 6 o 6 o __ C r Per Cent. __ 0.5 0'4 0'4 0.4 0.25 0'2 0'2 0'2 0'2 0'1 0'1 0.1 0.05 0.05 - 0. 12 12 12 10 12 12 I0 12 10 10 -- S' Per Cent. 10 - 3. 9'70 12-98 15-55 19-93 9'76 38-1 13 *88 16-54 19'68 31-15 8-80 35'3 3'47 31-25 t . c,. c,. g,. --___-- h. m. 27 o 8.0 20.61 2.473 50 30 4.0 24.9 2-99 27 o 4'0 8.08 0.969 17 30 2.0 3-86 0.386 20 10 2.0 3-82 0.46 50 30 2.0 11-38 1.366 27 o 1.0 2-69 0.269 50 30 1.0 5-88 0.588 I7 30 1'0 2'73 0'273 20 10 1'0 1.55 0.186 V..- I2 I2 I2 I 0 I2 I2 I0 12 I0 I0 24'5 6.9 6.9 6-9 13'3 13'3 3'5 3'5 3'5 3'5 0.179 0'730 0.476 0.0494 0.715 0.465 0'0490 0*710 0'463 0'0492 0.712 0'464 0.0234 0.670 0.440 0.0256 0-732 0'478 0'108 0.813 0'532 0.071 0'530 0'346 0'035 1'00 0.650 0'020 0'572 0'372 A. Per Cent. - I00 100 I00 I00 I00 I00 I00 I00 I00 96 96 96 76 76 - E. Cal. 10 - 5. -- 2-72 2'57 2-25 2'36 2.72 2-64 2-57 2-25 2'36 2'64 2-25 2'44 2'54 2 *60 V. c.cm. 0. cm.2. g,. 10- 3. 4. 10-5. '658 '700 '755 '778 '671 -720 '748 '800 '765 '615 '748 -628 '660 '526 t. 9 IP. - '503 '532 '575 '595 '511 '550 '572 -610 -582 '4 70 '570 *480 '505 '402 - NO. IVb. Vb. VIIa. 1Xn. IVa. 111). Va. VIIb. IXb. IIU. VIIIa. VLIIb. Xu. Xb. h. m. I 0 I 20 2 0 I 0 I 20 2 0 I 0 I 41 3 40 1 41 3 40 4 25 0 30 5 30 1'455 1'95 2'333 2 '99 1.464 5 '70 2.082 2.48 2'95 4'67 1-32 5'295 0.521 4.688 .- -658 '700 '755 '778 '671 -720 '748 -800 '765 '590 '719 '603 '502 '400 TABLE 11. Hg 405; p = 1-42.10-s. __ NO. - E. - I *96 1-96 1.89 2-32 2-36 2.36 2-36 - A. - 4. ~~ g,. corr. 6.795 6-17 6-38 5'41 6-32 6.29 5-19 V. W P * 4 I . 1-1-1- 0.680 0'635 0.610 0.476 0'507 0'543 0.450 la. Ib. 11. 111. IV. Vb. Va. - 2'0 I '0 1'0 1'0 1.0 1'0 0.5 j 46'7 142'25 43'75 37'35 43'6 43'2 35'65 7'005 6'34 6.568 5'603 6'54 6 -48 5'35 0.700 0.752 0'723 0'550 0.600 0'645 0.741 97'5 84 *4 84'4 84'4 84.4 84'4 60.6 0'490 0.525 0.508 0.390 0-423 0'455 0-522 [o-5. E. 0.78 0'835 0.78 0-82 0.71 0.82 0.71 0.78 0'835 0.835 -___ NO. I Va. VIa. Vb. IIIb. IVU. Vlb. IIIU. 1Vb. vc. VIC.456 CONFIRMATION OF EINSTEIN LAW Symbols in the tables : V the volume of the reaction system in C.C.0 the radiated surface in cm2. t the time of insolation in hours and minutes. C, the initial concentration of the aldehyde in per cent. C, the concentration of the acid after the insolation in per cent. x IO-~, indicating also the reduction in the concentration of the aldehyde. g, the amount of acid in g. x I O - ~ formed in the light. gs COrr (for Hg 405 only) a corrected value because in the neigh- bourhood of 405, the line 436 exerts its influence. The total amount found analytically, was corrected by means of the directly determined blue reaction. E the incident energy in cals. x X O - ~ per second per sq. cm. A the energy in per cent. absorbed by the reaction system.4’ the photochemical yield per the incident energy. 4 the effective photochemical equivalent of E. Warburg. $ the fundamental photochemical equivalent is given at the head of +/’ the quantum efficiency of E. Warburg. The results in the three tables have different weights, and indeed the most precise are for Hg 366, in which are obtained in a few hours, ac- curate analytical values for the acid content. The experiments extending over nearly six hours in Hg 405 show somewhat greater uncertainty owing to the larger fluctuations of light intensity, and above all to the fact that the definite value of the change and the energy computation had to be deter- mined by subtraction of the blue values. The experiments in the blue (Hg 436), on account of the weak absorption of this spectral region, had finally to extend without interruption over several days.I t is here that strong light fluctuations and impurities in the very sensitive solvent can introduce large errors in the measurements, in addition to which the very weak absorption is easily changed by slight impurities. These are the conditions under which quantitative photochemical and energetic experi- ments have never previously been carried out. I t will be observed from the final columns that the quintum efficiency in all cases comes out in the neighbourhood of 0.5. The deviations lie within the limits of error of the necessary measurements. The decrease of the yield in the quite small concentrations of the a-nitrobenzaldehyde in the ultra- violet experiments of long duration, must be explained by the gradual transformation of the aldehyde into the acid, because from the measure- ments of Hyman the a-nitrobenzoic acid is an equally strong absorber, with the effect that a part of the radiation is withdrawn from possible chemical action.Having regard to this, the value of the quantum efficiency would be raised in these cases also to the normal value of 0.5. T h e efficiency ratio in all the three spectral regions taken, is therefore equal to +, and it follows that we can take the Einstein law for the case under investigation as proven. The deviations of the value n from I in the proof of the law, give the basis for substantiating a conjectured mechanism of reaction. I n this way E. Warburg1 was able to deduce from the measured value 2 for the efficiency ratio in the photochemical decomposition of hydrogen each table.1 E. Warburg, Beyliner Akad. Ber., 1916, 314 ; 1918, 300.DR. FRITZ WEIGERT AND DR. LOTTE BRODMANN 457 bromide and iodide, that through secondary reactions an affected molecule leads finally to the decomposition of two molecules. The extraordinary fruitfulness of this supposition of hypothetical inter-reactions, following the example of E. Warburg, is indeed evident in the whole of modern chemical kinetics. Our finding + for the efficiency ratio would now lead to the supposi- tion that two quanta are required for the transformation of one molecule of o-nitrobenzaldehyde. But we must decline this interpretation on the following grounds. First, we know nothing about the specific mechanism of the primary photochemical process.If we suppose quite generally that by the absorption of one quantum, a molecule of the aldehyde is transformed into the active condition, then this activated molecule would have to absorb a second quantum during its period of activity, But this second absorption is extremely improbable, because the concentration of the onefold acti- vated molecule is very small, and because the normal aldehyde would lay claim to the light principally for itself. In addition, a twofold activation demands unconditionally an influence of the concentration and of the wave- length on the quantum efficiency. I t was found, however, that in an interval of concentration from 0.05 to 8 per cent., hence from I to 160, only the normal optical effect of the concentration was observed.' In the same way it is improbable that two once-activated molecules, produce one molecule of the acid at their first encounter, and even this supposition would permit an influence of concentration.The primary absorption of the quantum has the effect of making possible the transport of one atom of oxygen from the nitro to the aldehyde group. I t can now be assumed with certainty, following the known experiences on the directing photo- chemical actions of linear polarised light,2 that in the primary quantum process a definite direction asserts itself, and that the transformation into the o-nitrosobenzoic acid only occurs when this direction corresponds with the connecting line between the nitro and aldehyde groups. To obtain a picture of this directing bond one may suggest that at first a photoelectric electron from the aldehyde group must cross over to the nitro group. This electron transition, however, is to be taken only as a symbol for a directed primary process.An effective absorption leading to further change, occurs only when the electric vector of the incident radiation harmonises with this connecting direction. Now one can assume that the irregular molecules of the aldehyde present in solution, from the point of view of the kinetic gas theory, are arranged in three principal directions at right angles, where each direction corresponding with the connecting line (A-N, group N) takes f: of the molecules. We now propose the following conception. ildehyde group A-Nitro- f e I A-N ; __ i _ , Incident beam of light.2 3 A A 1 ; / N N An incident polarised ray from the left whose rectangular direction of vibration is e, is not absorbed by molecules I at all, is effectively absorbed by 2 , but not effectively by 3 because the electron hypothetically ejected in the direction e would not encounter the nitro group in the position 3. 1 The extinctions vary between 0'0153 and 6'1. 2 F. Weigert, Ann. der. Physik., 63, 681, 1920.458 CONFIRMATION OF EINSTEIN LAW Hence we measure the absorption of $ of the molecules present, but only + can lead to chemical change. The same applies to natural light which one can imagine as a mixture of light polarised in all directions. This conception leads directly to an efficiency ratio +, which was found experimentally. I t might be tested by photochemical research on similarly oriented o-nitrobenzaldehyde molecules, such as in solid crystalline sub- stances.This research has been carried out following a method of F. Weigert l several years ago by M. Padoa,2 in which he investigated the decomposition of single clear crystals of o-nitrobenzaldehyde in polarised light. In that work it was established that there were distinct differences in the speed of reaction according to the orientation of the crystal to the plane of polarisation, so that the assumption of anisotropy for the single solute molecules is quite a probable one. The research described above, on the condition of the correctness of these conceptions, would show for the first time, that the vector action of the light in the primary process of the chemical reaction, can occur not only in solid layers but also in weak solutions. The means for carrying out this research were placed at our disposal by the Hoshi Institute (Japanese Institute for assisting German science) and for this help we express our deep thanks. Note added to prooj-We take the opportunity to mention that before our own measurements were made the equivalence law was twice tested in the case of the reaction of Ciamician and Silber. The first time by Kum- merer (Dissertation, Berlin, I g 14, S. 64) in an acetone solution by a radio- calorimetric method and the second time by Bowen, Hartley and Scott (Journ. Chem. SOL, 125, 1218, 1924) in solid aldehyde using an air- thermometer as a radio-calorimeter. In both cases the Einstein law could be confirmed as regards the order of the effect. As the experi- ments have only been tried with a few wave-lengths and the experimental methods were not very accurate, these measurements cannot be con- sidered in a special discussion on photo-chemical reactions. 1 F. Weigert, Zeitschr. f. Electrochcmie, 24, 222, 1918. 3 M. Padoa, R . Accud. dei Liltc (5), 28 (2), 372, 1919.

ISSN:0014-7672    

DOI:10.1039/TF9262100453

出版商:RSC    

年代:1926

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. THE RELATION BETWEEN QUANTUM SENSITIVITY AND INTENSITY OF RADIATION.BY PROFESSOR CHR. WINTHER (COPENHAGEN). Received August 4fh, I 9 2 5. The intense work of the last few years has shown the immense impor- tance of quantum sensitivity as a measure of photochemical sensitivity and as a means for examining closely the mechanism of photochemical re- actions. Therefore, the time has come for examining the factors on which this quantity depends. I n most investigations only the concentration of the sensitive substance is altered, and many cases are known in which the quantum sensitivity varies considerable with the concentration. In a few cases the radiation energy is altered too, but after a close inspection of the literature, I have found only one case in which attention has been paid to the influence of the temperature.l All the other known temperature coefficients of photochemical reactions are based on the measurement of the incident radiation, and no account has been taken of the very frequent variation of the absorption with temperature.Now it is an important fact, that in the few cases where the energy has been varied, the quantum sensitivity is either constant or vanes in such a way that the relation between the two quantities has always the same form. The known cases of the latter kind are the following, in chrono- logical order :- ( I ) Decomposition of Ozoize.2-Moist mixtures of ozone and oxygen. tz = quantum sensitivity, Eabs = the absorbed energy. VOl. Per Cent. 03. 10.~0 6-56 4'47 2'49 2-23 1-30 0.80 Eabs. 102 I 18 I06 253 96 I 06 83 12. 4'70 3'69 3-17 2'1Q 3-08 2.07 I -66 Vol.Per Cent. 03. 8-15 7'93 6.27 5 '63 Eabs* 126 388 433 138 It. 6.58 3-82 2-40 5'09 - - The large values of energy give in all three cases (the underlined numbers) small values of n. (2) Decomposition of Hydrogen Peroxide in Aqueous &Zution.-From the measurements of Henri and Wurmser3 one extrapolates for the wave- length 31 I pp and concentration 0.049 : iv = 2'9. 1 2 Warburg, Sitz. preuss. Akad. Wiss., 1913, 644. 3 Compt. rend., 157, 126 (1913). 459 Decomposition of NH3," Kuhr, Compt. rend., 178, 708 (1924).460 QUANTUM SENSITIVITY AND INTENSITY OF RADIATION The measurements of Kornfeld give for the same wave-length and con- cen tration : but Henry and Wurmser used a much more intensive radiation than did Miss Kornfeld. (3) For photosynthesis in green leaves Warburg and Negelein2 have found that n decreases with increasing energy.(4) The oxidation of hydrogen iodide in aqueous solution has shown just the same feature as the other three cases.3 The following table con- tains, as an example, the values for 366pp and about I - n solution. = 43'4, Eabs 320 294 254 240 227 207 220 Eabs I 63 154 154 = 47 87 80 48 n. 14'3 14'9 15.1 I 2.4 20.7 21.9 23.1 -~ Eabs 45 23 23 23 9'3 9'3 n. 21.8 51'7 3 7'3 42'3 51'9 83-0 (5) For the reaction between potassium oxalate and iodine or bromine the velocity has been found4 to be proportional to the square root of the energy. In all known cases then, the quantum sensitivity is either constant or de- creases with increasing energy. So far as these facts have been known, they have mostly been explained as exhaustion phenomena.For the oxidation, at least, of hydrogen iodide, which has been the most thoroughly examined of the four cases, this explanation does not hold. First, the speed of stirring, when a minimum speed has been reached, has no influence on the results. Secondly, the solution contains very much more oxygen than the total reaction (in light and darkness) consumes every second. Thirdly, for the wave-length 366pp, by increasing the energy a point was reached where the oxidation was constant and independent of further increase of energy. But for other wave-lengths, e.g, 436pp, under the same conditions much more iodide was oxidised, so that the oxygen was not nearly used up in the experiments with 366pp. As regards the decomposition of ozone and of hydrogen peroxide, where no second substance is necessary for the reaction, the hypothesis of exhaustion is equally untenable.For photosynthesis the whole process is so complicated that it cannot be said whether exhaustion is possible or not. I t has been said that all reactions, even those that appear simplest, are in reality so complicated that they must at first be divided into series of partial reactions, before anything can be done to find the true value of the quantum sensitivity. Until this work has been done, one must be allowed to try whether a simpler method of working might not give some information about the mechanism of sensitivity. For the oxidation of hydrogen iodide I have tried this, on the assump- tion that only those molecules (or &-ions) which take up one quantum are thereby brought in such a condition that, in one or other way, they give Possibly this is true.12. wiss. Phot., 21, 66 (1921). 3 Winther, 2. p h j s i k . Chenr., 108, 236 (1924). 4 Berthoud, Bellenot. Helvetica chim. Acta., 7, 307 (1924). 22. physik. Chent., 102, 235 (1922).PROFESSOR CHR. WINTHER rise to the formation of iodine. The ions which take up two or more quanta are, on the contrary, not brought to such an active condition. I am fully aware of the physical improbability of this assumption, but have considered it worth while to try calculating on this basis. I have thus obtained a formula which accounts very well for the observed facts and, moreover, gives some information about the character of the light absorption, the partition of energy amongst the I,-ions, and other matters of some significance.Further, some observations of Warburg, and of Griffith and MacWillie on the decomposition of ozone, of F. Weigert on the QS oxidation of chinine, fluoresceine, erythrosine and potassium-ferrocyanide, and of Ewan on the oxidation of phosphorus can be calculated on the same basis. Further investigations must show as to whether these assumptions hold good, or whether other lines of work may be more profitable, but, above all, future investigators must necessarily take into account-and explore- the variation of quantum sensitivity with energy, before any conclusions can be drawn about the real value of the quantum sensitivity and its relations to other factors.8' i i c i i o $9 (6 i a zo (2 t i Zb u w u w i b . .w EEW FIG. 2. At this moment I will only draw attention to one point, namely, the relation to the wave-length. Warburg has, for the dissociation of hydrogen iodide, found that the quantum sensitivity is independent of the wave-length between 207 and 282. He has, indeed, worked with the same energy for each of these wave-lengths. Possibly his result is true, but as long as nothing is known about an eventual variation of the quantum sensitivity with energy, this cannot be said with certainty. My own measurements on the oxidation of hydriodic acid have given Sitzb. kgl.preuss. Akad. Wiss., 1918, 310.462 QUANTUM SENSITIVITY AND INTENSITY OF RADIATION the values, plotted in Fig. I , for the quantum sensitivity for a normal solution.Abscissz are the absorbed energies, ordinates the quantum sensitivities. The diagram shows the values for five wave-lengths, namely, 436, 405, 366, 313, and 280. Plotted in this way, the values all lie on the same curve, i.e. the quantum sensitivity is independent of the wave-length. Again, in plotting the quantum sensitivities, not against the absorbed energy but against the number of quanta absorbed, we get the diagram shown in Fig. 2. Here the coincidence is not so good as before. The values for 436 and 405 lie higher than the corresponding values for the other wave-lengths. As shown by the extinction curves in Fig. 3, which were measured by m y photographic method,' the extinctions for 436 and 405 are smaller than for I 15,000., 10,000 1,000, the other wave-lengths. to give the best agreement with the Einstein law. measurements will therefore be necessary : The former method of plotting, therefore, seems For the thorough examination of a photochemical reaction the following I. The absolute energy values of the incident radiation. 2. The extinction coefficients of all examined systems for all wave- 3. The velocity of reaction of the pure photochemical process for If this programme could be accomplished for a series of different re- lengths used. different values of radiation and wave-length. actions, the laws of sensitivity could probably be found. I z . wiss. Phot., 22, I25 (1923).

ISSN:0014-7672    

DOI:10.1039/TF9262100459

出版商:RSC    

年代:1926

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No.13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions.Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. THE LAW OF PHOTOCHEMICAL EQUIVALENCE AND THE PLACE OF THE QUANTUM THEORY IN RELATION TO THE ATOMIC THEORY AND ENERGETICS. BY PROFESSOR DANIEL BERTHELOT (PARIS). TRANSLATED BY H.BORNS. Communication received August 2 6th, I g 25. Within recent years the law of photochemical equivalence has received several confirmations and has been presented in some of these cases as exact, in others as grossly erroneous. The quantum theory has on the other hand been considered even by its most eminent protagonists as altogether revolutionary and as contrary to the classical principles of science. I believe the law of photochemical equivalence to hold rigorously, provided we define the conditions of its applications precisely. There is nothing new about these conditions which were precisely defined in 1865, as dominating the whole of photochemistry, by Marcellin Berthelot. On the other hand, I think that the fertility of the quantum theory, notably in chemistry, lies in the fact that it finds its place naturally in the classical frames of energetics and atomistics.I explained before the International Congress, held at Brussels in 191 I for the purpose of discussing the quantum theory, my view concerning these matters in an article, published on April 30, 191 I, in the Rev. Gin. des Siences, on “The Chemical Effects of Ultra-violet Rays,” and particu- larly in Part IV. of this article on “Thermodynamics of Ultra-violet Radiations : the Photochemical Potential.” That view is based on the distinction of the two factors (capacdty and tension) of the radiant energy, and on the novel conceptions of radiant entropr and of phtochmical potentiaZ, parallel to the classical conceptions of thermal entropy and of electrical potential.I developed these ideas in my paper on “Ultra-violet Radiations,” and subsequently in several notes presented to the AcadLmie des Siences; further in my communications to the Soc. ELanf. de Phys. (March I, 1912) on ‘‘ Photochemical Effects of Ultra-violet Rays,” and (March 5 , 1915) on “The Relation between Radiant Energy and other Forms of Energy ; ” in my memoir on “The Reciprocity of Electrical and Magnetic Phenomena ; the Elementary Discontinuous Factors of Energy ” ; I n my opinion matters are less complicated. 1 Bull. SOC. Inglrt. Civils, Dec. 1911. 2’‘ The R61e of Wave-Length in Photochemical Reactions,’’ C.R., 1% 1597, 1912 ; ’@ Kinetics of Photochemical Reactions,” 160, 519, 1915. 3 Bull. SOC. Internat. Electr. 131 2, 53 and 55, 1916. 463464 PHOTOCHEMICAL EQUIVALENCE & QUANTUM THEORY in my paper on the “Chemical Aspect of the Quantum Theory and the Thermodynamics of Photochemical Reactions,” and on “ The Quantum Theory from the Chemical and Thermodynamical Standpoint.” The Two Factors of Radiant Energy, the Factor of Capacity (Radiant Entropy or Action), the Tension Factor (Vibratory Frequency or Photochemical Potential).According to the ideas of Rankine and Maxwell, developed particularly by Gibbs and H. le Chatelier, every form of energy may be represented as the product of two variables, one of position, the other of tension. The former may be called capacify factor (or extension factor) ; the other tension factor (or equilibrium factor or energetic potential). Form of Energy. Tension Factor.Capacity Factor. Superficial, AS. Surface tension, A. Surface, S. Volumic, PV. Pressure, P. Volume, V. Thermal, 02. Temperature, 0. Thermal entropy, 2. Electrical, EQ. Electromotive force, E. Quantity of electricity, Q. Radiant, NH. Frequency of vibration, N. Radiant entropy, H. Chemical, @M. Affinity (chemical potential), a. Number of molecules, M. The essential function of the tension factor is regulation of the equilibrium. In order that two systems be in equilibrium, they must have the same tension. This factor is independent of the mass of the systems. The capacity factor, on the other hand, is proportional to the mass of the system. Doubling the mass, means doubling its volume, its entropy, the quantity of electricity, etc. One of the direct consequences of this property is the following.When we have determined the numerical value of the energetic capacity of a system with respect to the gram-moZecuZe or mol. in accordance with actual chemical practice, it will suffice for the purpose of referring it to the true molecule and of obtaining the elementary value to divide the former value by 60.6 x 1 0 2 ~ (Avogadro’s number). In the table given above the two factors of the radiant energy are defined in accordance with the theory which I outlined in my paper of April, I g I I . I showed that my numerous photochemical experiments (published in the C.R.) enabled me to assign to the vibratory frequency the r61e of tension factor or of photochemical potential. As regards the second factor I proposed the name radiant entropy on account of its analogy to thermal entropy I showed in fact that the degradation of the radiant energy is governed by a principle analogous to the principle of Carnot.Just as the maximum work done by a heat engine operating between the temperatures T2 and T1 is equal to I - T1/T,, so the maximum work of a radiant machine operating between the frequencies N, and N, is equal to I - NJN,. This conception of the phenomena enables me at once to answer a question which Nernst and G. Lemoine have considered one of the most interesting of photochemistry, viz., which fraction of the radiant energy is utilisable, i.e., can be transformed into mechanical work ? The rale which Carnot’s principle assigns to temperature in the case of the heat engine is taken by trequency in the case of the radiant energy engine.These views have later been confirmed by Maurice and Louis de Broglie in their X-ray 1 Bull. SOC. Chimique de France [4], 35, 241-302, March, 1924. Bull. SOC. InKktt. Civils, May-June, 440-4789 1925.PROFESSOR DANIEL BERTHELOT 465 studies.' I t will be seen that the quantity which I call radiant entropy is nothing but the action of Hamilton and of Planck. The use of the term entropy has, in my opinion, the advantage that it indicates at once, by virtue of notions now classical and familiar, that the quantum conception marks a departure from rational mechanics as based upon reversibihty for the same reasons which render the Carnot principle irreconcilable with those of mechanics. The atomic structure of matter implies this statistical irreversibility which is expressed by the so-called law of large numbers.The Law of Photochemical Equivalence. Special Case of the Law of Equivalent Molecular Capacity. Physico-Chemical Significance of Planck's Constant : its analogy with Faraday 's Constant. The study of the capacity factors of different forms of energy shows that they obey the same physico-chemical law which (in my paper contributed to the Sac. Ikternat. EL!, I g I 6) I proposed to call the law of equivalent mode- cular capacities. According to this rule, whatever the form of energy in question, adl chmical units (molecular atoms) have the same energetic capacify indtyendent of the nature of the body. I n particular this proposition finds expression in the law of equivalent volumes ufgaseous bodies of Gay-Lussac, which is the basis of atomic nota- tion, and in the law of edectrochemicaZ epuivalente of Faraday.When a chemist writes an elementary equation such as : I vol. hydrogen + I vol. chlorine = z vol. HCl. z vol. hydrogen + I vol. oxygen = z vol. H,O. 3 vol. hydrogen + I vol. nitrogen = 2 vol. H,N, it is implied that there exists, for gaseous bodies, the same unit volume for hydrogen, oxygen, chlorine, nitrogen, etc. Referred to the gram-molecule at N.T.P., this volume is I 1,206 ~ r n . ~ I n the same way one valency-gram of any metal, K, Na, Ag, Cu, Au, etc., carries in electrolysis the same quantity of electricity-g6,500 coulombs. The quantum notion is nothing but the law of equivalent molecular capacity in a form applied to radiant energy.Photodysis or decomposition by light is parallel to electroZssis or decomposition by electricity ; a valency- gram there transports always the same quantity of radiant entropy (or of action, if that word be preferred), equal to 4 x I O - ~ erg-seconds. This quantity of entropy can be measured in a photolytic process just as the quantity of electricity is measured in an electrolysis. In order to study the electrolytic decomposition we gradually raise the electric tension at the terminals and we determine the minimum tension required for this purpose ; that is the tension at which the phenomenon is reversible. The energy ex- pended is equal to the product of this tension and of the quantity of electricity applied. Similarly to study the photolytic rupture we increase the radiant tension, i.e.the frequency, up to the moment when photolysis sets in. The energy ex- pended is equal to the product HN, the factors being frequency N and quantity of radiant entropy applied H. I have made a particularly careful study of the constants of one photo- lytic decomposition, that of the ketonic sugars and notably of levulose.2 At this tension the phenomenon is reversible. ' C . R . Dec. 2, 1921. a A levulose actinometer, C.R. 156, 707, March 3, 1913.466 PHOTOCHEMICAL EQUIVALENCE &. QUANTUM THEORY The photolysis sets in exactly at wave-length 0*30p, corresponding to frequency N = 1 0 ~ ~ . In order to determine the radiant energy consumed, we have to estimate, by photometric and chemical measurements, the luminous energy of the mercury lamp used, the fraction of this energy which is of wave-length less than 0.30~ and the portion absorbed by the solution and concerned in the chemical transformation.Details of this research will be found in my paper sent to the Soc. Chim. mentioned above. The result is the following : The radiant energy required for the breaking- up of one vdency-gram is W = 4 x 1o12 ergs; the corresponding radiant entropy is H = W/N = 4 x I O - ~ erg x second. This number is the photolytic constant, analogous to the electrolytic constant 96,s 00 coulombs (9650 c.g.s. units). The figures so far given are referred to the gram-molecule; to refer them to the true molecule we have merely to divide them by 60.6 x 1022. The electric charge per gram equivalent being 9650, the elementary charge will be 1.59 x I O - ~ O c.g.s.unit. The gaseous volume per gram equivalent being 11,2c6 ~ m . ~ , the elementary volume will similarly be 1-85 x 10-20 ~ r n . ~ . I t follows from these considerations that combination and decomposition in gases take place in jumps by multiples of 1-85 x 10 - 2o C M . ~ at N.T.P. The phenomena will never be observed with smaller volume variations and the figure deduced really represents the elementary volume. Thus normal ebullition of a liquid consists of the jerky emission of small bubbles of vapour which at normal temperature and pressure would have the volume I -85 x z x I o - 20 ~ m . ~ The growth of the gaseous volume is discontinuous. Heating a liquid by an external source will not evolve any bubbles, not half or a quarter of a bubble until the energy supplied is sufficiently strong.Then one bubble is liberated, more energy is absorbed, more bubbles are evolved, and so on. Whatever the liquid evaporated, the volume of each elementary bubble is the same. The source of electricity sends energy in bundles or parcels to the electrodes; when the supply is sufficient, a first ion is detached which carries a quantity of electricity equal to 1-59 x 10 -20 ; a second ion cannot be liberated before a second parcel has arrived. As in the case of evaporation the elementary unit of energetic capacity, ie., in this instance the electric charge, is in- dependent of the nature of the body. Electrolytic decomposition takes place in similar jumps. The Law of Definite Proportions.Matter Imposes the Discon- tinuity of its Atomic Structure on the Capacity Factors of the Diverse Forms of Energy. All these discontinuities are a consequence of the fundamental discon- Chemical notation is based upon the law of definite The series of compounds tinuity of matter. proportions which is itself a discontinuity law. which two bodies, e.g., nitrogen and oxygen form : N@,, N01, NO,, Nos, Nod, NOS, is not a continuous curve, but a stairway of six steps. The discontinuity is particularly striking when we compare the gas volumes on the ground of the simple relations of Gay-Lussac. One volume of nitrogen combines with I, 2, 3 volumes of oxygen, but never with a fractional volume. I t is natural to assume that this chemical discontinuity, which is an expression of the atomic structure of matter, must be traceable in the physical laws.PROFESSOR DANIEL BERTHELOT 467 Long ago Marcellin Berthelot recognised that, when physics would descend down to the elements of matter, that is to the atoms as chemistry does, it would likewise have recourse not only to differential calculus, which is the science of continuity, but also to the processes and symbols of arithmetic, which is the science of discontinuity.We are at present witnessing this evolution in the quantum theory and its application to the lines of the spectrum. But, contrary to what is too frequently repeated, the theory of quanta does not upset our conceptioni of the natural laws: it is simply the form which the atomic discontinuity takes in the domain of vibratory energy.Matter h s a discontinuous structure and it imposes this discon tinuity, not upon energy itsell: as is often stated erroneously, but on th capacity factors by which the diverse forms of energy mangest thrnsehes. Since there are elements of matter or atoms, there are also elements of space, elements of electric charge, elements of surface, elements of thermal entropy and of radiant entropy. The mechanism of radiation by quanta as discovered by Planck does not in any way differ from the mechanism which we have outlined for evaporation and electrolysis. All these pheno- mena (evaporation, electrolysis, radiation) consist of a liberation in steps, not of atoms of energy, but of atoms of energy capacity. In the case of radiation, as in those of vaporisation and electrolysis, it is sufficient to divide by 60.6 x 1022 the number H = 4 x I - o - ~ erg-seconds, found above in the photolysis of a gram-molecule, in order to arrive at the quantum h = 6.55 x I O - ~ ~ erg x second, referred to the true molecule.From the historical standpoint it is curious to note that, in the cases of the elastic energy of gases and of electric energy, the quantum was first discovered as referred to the gram-equivalent, and that the hue quantum referred to the atom was deduced by dividing the value by 60-6 x 1 0 2 ~ . I n the case of the radiant energy the contrary applies. The true quan- tum referred to the atom (the Planck constant h = 6-55 x 10-2') was first found, but this by an accidental calculation, which was so unexpected that the Brussels Congress of 191 I discussed for a long time the meaning which it should attribute to this quantity without succeeding in defining it clearly.The illustrious president of the Congress, H. A. Lorentz, more- over, did not indulge in excessive illusions when he said in his inaugural address : " I shall admit that what we contribute to immediate progress does not amount to much. In fact this progress is due more to individual efforts than to the deliberations of the Congress." The constant of Planck, the meaning of which seemed so enigmatic to the members of the Brussels Congress, appears then to be the elementary photochemical constant, analogous to the elementary electrochemical con- stant of Faraday. Just as the latter is the atom of electricity or el'ecfron e = 1.59 x I O - ~ " so the former is the atom of radiantentropyh= 6-55 x 1 0 - 2 ? I have proposed to call this unit the radion.The term has the advantage over the term quantum of not being equivocal ; for owing to the confused ideas and the groping of which I have spoken the word quantum is used to designate sometimes an element of action, sometimes an element of energy, and there exists an infinity of quanta of energy whilst there is only one quantum of action. The physical meaning of the element of discontinuity h appeared mysterious for a long time. Ylanck saw first an element of energy in it and, if he was later induced to recognise it as an element of action, that was not done on account of some initial reasoning based upon468 PHOTOCHEMICAL EQUIVALENCE & QUANTUM THEORY the idea of an element of energy but, apart from all theoretical considerations, simply not to put himself in contradiction with the principle of Carnot.Lorentz remarked: “From the historical point of view the element of energy takes priority over the element of action.” I t is moreover well known that, just as the value of the electron as deduced from the chemical equivalent has subsequently been met with in a multitude of optical, magnetic and radioactive phenomena, etc., in the same way the value assigned to the radion by the law of photochemical equivalents reoccurs in measurements of radiation, specific heat, spectrum lines, photoelectricity etc. The Necessity of Excluding Spontaneous Irreversible Reactions in Verifications of the Law of Photochemical Equivalence.Before leaving this part of the subject it will be useful to say a few words concerning the objections to the validity of the law of photochemical equivalence raised on account of certain experimental discordances. The law may be enunciated in the following terms : In any reversible photo- chemical reaction, whatever be the compound in question, the breaking-up of a valency corresponds to the liberation of the same quantity of radiant entropy. Or again: The appearance (or disappearance) of a material chemical unit (molecule) is linked with the appearance (or disappearance) of a unit of energetic capacity, that is, a unit of radiant entropy (radion). That this may be so, the reaction must be reversible; that point I have already emphasised.I t is not otherwise in the case of Faraday’s law; that law can be verified, eg., by the decomposition or recomposition of water (in a voltameter or gas cell). We should, on the other hand, only arrive at illusory results in repeating the experiment with an irreversible reaction such as the decomposition of water oxygenated at ordinary temperature. Let us consider a photochemical reaction which was studied early in the nineteenth century by Berthollet, Gay-Lussac and ThCnard, the com- bination of hydrogen and chlorine. Exposure to ultra-violet radiation will start the reaction in this explosive mixture. The illumination acts like a trigger; there is a tendency to combination, but it is opposed by passive resistances. In this case there is no relation between the quantity of radiant entropy supplied by the ultra-violet radiation and the quantity of chemical compound formed.Now in 1865, Marcellin Berthelot pointed out that the whole of photo- chemistry is dominated by an essential distinction on which he has frequently insisted.’ The first are of the exothermic type and tend to arise spontaneously. (‘ The light,” he said, “here acts like a match which lights a bundle of firewood.” The second are of the endothermic type. They are reversible reactions; the light supplies the energy necessary to raise the chemical level. H e selected a few reactions (decomposition of nitric or of iodic acid by solar rays) in which the chemical work done by the light could accurately be estimated. These reactions are relatively rare in the range of visible light; but my studies in the ultra-violet have enabled me to multiply their numbers.The objections raised against the law of photochemical equivalence are in general There are two kinds of chemical action of light. 1 Revile des Cows publics, 1865 : Novel Researches in Thermochemistry ; Endo- Ann. de Chinz. 18, 83, thermic and Exothermic Reactions‘ ; Chemical Effects of Light. 1869 ; Essai de MCcanique chimique, I. p. 20.PROFESSOR DANIEL BERTHELOT 469 due to a non-understanding of this fundamental distinction between irreversible spontaneous reactions and reversible reactions. lnsufficiency of Verifications of the Law of Photochemical Equi- valence based upon Heat of Reaction. More serious objections can be taken to the mode of calculation adopted in most of these verifications.I consider it useful clearly to put this point, for many authors do not even appear to suspect it. A correct calculation of the radiant entropy demands an exact evaluation, by photochemical and chemical means, of the radiant energy of the source and of the energy utilised in the chemical reaction, as well as of the photochemical potential of the reaction. The manner of the calculation has already been indicated. In the majority of cases support of the law of photochemical equivalence has, however, been based upon the use of a more rapid method which relies upon the heat of reaction, determined either directly in a calorimeter or even deduced from certain physico-chemical relations. These verifications lack convincing force.Sir William Thomson, it will be remembered, proposed to calculate the electromotive force of the Becquerel-Daniel1 cell and thus indirectly to confirm the law of Faraday thermochemically by starting from the heat of formation of zinc sulphate and of copper sulphate. His argument presumed that the whole chemical energy was transformed into electrical energy. But Gibbs showed subsequently that the calculation could only be accurate in cases where the two quantities E and E - 6E/6T could be substituted for one another, that is, if 6E/6'r = 0, and if the e.m.f. E were independent of the temperature T. From my note of March 5, 1 9 1 5 , ~ on the relations of radiant energy to other forms of energy, in which I gave the thermodynamical equations governing actino-capillarity and actino- electricity, etc., it follows that verifications of the law of photochemical equivalence relying upon heat of reaction could similarly be accurate only in cases where N and N - T6N/GT had the same value, i.e., if the photo- chemical potential N were independent of the temperature.But up to the present no sufficient attempt has, so far as I am aware, been made to take measurements in this sense; the verifications made must hence be regarded as mere approximations. The Three Fundamental Categories of Physical Magnitudes : Mechanical, Thermal, Electrical, and the three Corresponding Invariants of Capacity : Radion, Thermon, Electron. To complete this study I have to indicate which of the elementary dis- continuous factors of capacity of the diverse forms of energy possess the character of physical invariants.The element of gaseous volume V = 1-85 x 1 0 - 2 ~ ~ m . ~ is not of that nature, since it depends upon temperature and pressure. The equation of perfect gases PV = RT shows that the in- variant is the function PV/T, or R, which has the dimensions of entropy. Now in his classical paper of 1888 on Chemical Equilibria, H. Le Chatelier first pointed out tEat the thermal dissociations of various chemical systems yield fairly the same numerical values for the quotient L/T, that is, for the variation of thermal entropy (L being the latent heat of reaction and T the temperature). This demonstration helps us to recognise that the law of equivalent molecular capacities is applicable to thermal energy and that there is a law of thermochemical equivalence in analogy to the law of 1 SOC.Franc. Phyt. 31470 PHOTOCHEMICAL EQUIVALENCE & QUANTUM THEORY electrochemical and photochemical equivalence. The dissociation by heat or thermolysis is analogous to the dissociation by electricity or electrolysis and to the dissociation by light or photolysis. Every thermolysis liberates per valency-gram the same quantity of thermal entropy independent of the nature of the body. This quantity of radiant entropy is, as I have shown in previous publications, equal to + R when referred to the gram-molecule. I t represents, therefore, the calorific capacity of a monatomic gas, uiz. 2.98 cal. per deg., or, in mechanical units, 1-247 x IO* erg.per deg. By dividing this number by 60.6 x 1 0 ~ ~ we find the elementary quantum or the atom of ther?naZ entrojy, s = 2-06 x erg. per deg. For this atom s I have proposed the name Thermon on account of its analogy to the atom of electricity or electron e, and the atom of radiant entropy or radion h. I t is very remarkable that the same invariant s recurs in thermal phenomena. I showed in 1916 that the law of equivalent molecular capacity holds for the surface energy orkapillary energy, provided we do not consider a capillary membrane in the presence of the generating liquid- in which case the capillary tension A would depend upon temperature alone and be independent of the surface in the same way as the pressure of a saturated vapour is independent of the volume-but assume the whole liquid Ito be spread in a thin capillary coating (a monomolecular layer).Under those conditions, A representing the capillary tension, S the surface of the membrane, T the temperature and T, the critical temperature, the fluid conforms to the following simple formula, the characteristic equation ofthe cajiZZaryphase which is analogous to the equation of a perfect gas, AS = $ R(T, - T). I n this state of the monomolecular layer and under comparable conditions (equal surface tensions and equal departures from the critical points) a gram-molecule of any liquid whatever occupies the same surface. Thus we may speak of equivalence in surface in analogy to the equivadence in volume of Gay-Lussac, the eZectrochemicaZ equivadence of Faraday, and the photo- chemicaZ equivaZence of Planck and of Xinstein.We then find for the capacity factor of the capillary energy (that is to say, for the surface) a natural elementary unit ; but this unit varies with the temperature and the surface tension. Yet this constant K does not introduce a new invariant, since K = +r = $s. There are definitively only three variants: s, e, h. Each of these three invari- ants is characteristic of one of the great categories into which all physical magnitudes (mechanical, thermal, electric) may be classified from the stand- point of energetics. The mechanical magnitudes may be expressed as functions of three fundamental magnitudes. I t is customary to select length L, mass M and time T ; but three others, e.g., length, velocity, and force, might equally well be chosen.Thermal magnitudes cannot be expressed as functions of three mechanical magnitudes such as L, M, T. A further magnitude, of purely thermal character, is needed. The one generally selected is the temperature ; but some other thermal magnitude, e.g., entropy, might be adopted. Similarly electrical magnitudes cannot simply be expressed in terms of L, M, T. A fourth magnitude, electric or magnetic, is required ; preference is given either to the di-electric constant or to magnetic permeability. Of the three invariants e, s, h, the first falls into the category of the electrical magnitude, the second into the thermal, and the third into the mechanical magnitudes. These are the three capacity invariants of the The invariant function is AS/(T, - T) = K.PROFESSOR DANIEL BERTHELOT 471 electrical, thermal and vibratoiy energies.The three invariants are funda- mental and independent of one another; not one of them is reducible to the other two. It is noteworthy thst the theory of relativity which has led to a modification, in moving systems, of the magnitudes which were habitu- ally regarded as primordial, such as length or time, does not assail the invariance of e, s, A. I f the old mechanical ideas have not emerged quite intact out of the struggle with the novel conceptions, the old energetic conceptions have successfully resisted all attacks. The fact that the invariant h can be expressed as a function of the mechanical magnitudes L, M, T, induces us to reject the opinions which Lorentz and Planck gave expression at the Brussels Congress.’ Lorentz remarked : ‘< Too great importance should not be attached to the circumstance that h has the dimensions of action.The A has also the dimensions e2/V if e signifies an electric charge measured in electrostatic units. I f we replaced h by e2/V in the formula for the black radiation, we might have to think that the universal element which we are searching for should be, not a certain action, but a certain electric charge,” and Planck replied : ‘‘ I can on principle only concede this point. I t is possible that we may have to connect h with e and with V, or conversely e with h and with V.” Once we admit that A is the capacity factor of vibratory energy, expressed in terms of L, M, T, it is clear that h is of purely mechanical character and independent of all electrical magnitudes.I t may play a part not only in the phenomena of radiation but in other vibratory phenomena purely mechanical. The only restrictions to be imposed is that the phenomena be periodical and characterised by a frequency N, because it is this frequency which represents the tension factor of energy of which A is the capacity factor. We are therefore unable to give our signature to the opinion which Planck expressed at the Congress (p. 113) : “There is no doubt that inas- much as the hypothesis of quanta possesses a profound meaning, the element of action A must have a fundamental importance also for non- periodical phenomena, as Sommerfeld has already shown.’ ’ Kinetics of Electrochemical, Thermochemical, and Photochemical Reactions. The knowledge of the values of e, s, h enables us to solve important problems of molecular kinetics and to demonstrate (as I showed in ‘‘ Cin& tiques des Reactions Photochimiques,” C.X.160, 519, 1915) that the velocities which particles acquire, in mechanical, thermal, and radiant phenomena, under the influence of a difference in energetic level present a mutual remarkable parallelism. In elementary mechanics, a point of mass m and weight p raised to the level Z possesses the quantity pZ of potential energy. In free fall through a vacuum it acquires the kinetic energy +mu2, so that &mv2 = pZ and v = JzpZ/m. I n that expression p represents the capacity factor of gravity energy, the level Z represents the tension factor, and p/m the gravitational acceleration at the level considered, which is independent of the body.Under the influence of a sufficient potential difference the molecule is split into a part negatively electrified of mass m and electric charge e (corpuscle of J. J. Thomson) and a positive nucleus of mass M and electric charge - e. The electric charge one and the same for all bodies, is equal to 1-59 x I C - 2 0 ; Formulz of the same type result for the diverse forms of energy. 1 ‘‘ Thkorie du Rayonnement et les Quanta,” p. 131.4 7 2 PHOTOCHEMlCAL EQUWALENCE & QUANTUM THEOR the mass of the corpuscle, likewise the same for all bodies, is equal to omgo x I O - ~ ~ . When we accept this for the vacuum tube, the electric decomposition will be accompanied by projections from the electrodes in opposite directions of corpuscles and nuclei.Under the influence of the potential difference E the corpuscles are expelled with a force such that +mv2 = eE; v -- J2eElm; for a p.d. of 40,000 volts the velocity would be about 120,000 km/sec. hor the positive nuclei of mass M, the relations are +Mu2 = eE ; ZI = J Z / M ; in the case of the hydrogen nucleus, e.g., whose mass is 1850 times that of the corpuscle, the velocity, at 40,000 volts, would be 2 7 70 km/sec. A sufficient rise T in tem- perature splits the chemical molecule into two portions, a negative corpuscle of mass nt which, in a vacuum, would acquire a velocity such that mv2 = sT and v = J2sT/m, and a positive nucleus of mass M, the rela- tions being 3Mv2 = sT and 77 = ,/2sT/M.The quantity s = 2.06 x I 0-16 (the atom of thermal entropy) is independent of the nature of the body just as is e, the atom of electricity. Application of these formulz to hydrogen, for which M = 2-016/60*6 x I O ~ ~ , show that at the temperature of melt- ing ice (T = 273-1') the hydrogen nucleus would acquire a velocity of 1830 m/sec. which is sensibly the velocity which the kinetic theory ascribes to the hydrogen molecule. But apart from the movement of the nucleus we have also to consider the velocity of the corpuscle ; that velocity already calculated is the same for all bodies. The co-existence, in the usual phenomena of thermal agitation, of two different velocities, the one belonging to the nucleus the other to the corpuscle, manifests itself in the absorption spectra by the simultaneous presence of two characteristic conjugated bands, the one in the ultra-violet, ascribed to the corpuscle, the other in the infra-red attributable to the nucleus.The dissociation by heat or thermolysis is hence effected by a mechanism analogous to electrolysis or photolysis. The decomposition of a molecule, or the rupture of a valency, if that mode of expression be preferred, is accompanied by the consumption of an elementary unit of energetic capacity, independent of the nature of the body. The thermal dissociation, like the other dissociations, consists in the rupture of a valency and the splitting of a molecule into a negative corpuscle and a positive nucleus. One cannot, therefore, say that the term photo-electricity is particularly well chosen.The word seems to imply that the dissociating action of the light is exercised upon bodies by a mechanism peculiar to light. That is not so. The dissociating effects of heat and of electrolysis are enacted by the same mechanism. The chemical conception of valency appears to be inseparable from the conception of the electrical constitution of matter. The chemical forces are nothing but the old electrical forces of Berzelius. From the formuke deduced it results that, whatever the mode of energy, the velocity of the particles is equal to the square root of the double product of the tension and capacity factors, referred to unit mass. The theory of radiant energy above outlined, according to which the tension factor is the frequency N and the capacity factor is the radiant entropy h, indicates in tne same way that a particle of mass m having a charge h of radiant entropy, carries when brought up to the energetic level N a quantity of energy hN which, manifested in kinetic form, imparts to the particle a velocity v such that, in a vacuum,.+mv2 = h N , ZJ = JzhN/m.We arrive thus in a simple way at the energetic magnitudes of Einstein's photo-electric formula. As in the case of electricity and heat we should, moreover, give the analogous formula for the positive nucleus, into which the mass M would enter; but we have no experimental data regarding that point. I t is ~- - Let us now examine dissociation by heat.PROFESSOR DANIEL RERTHELOT 473 known that the velocities calculated are superior to those which the particles acquire under the available temperature gradients.Twenty years ago Gustave le Bon emphasised in his studies of the dissociation of matter and its transformation into energy that the dissociating effect of light is incomparably stronger than that of heat. The results mentioned, although confirmed by experiment, have often been considered very surprising. ‘‘ They were not at all what was expected on the ordinary theories,” Einstein wrote in 1 9 ~ 2 , ~ “one would think that a certain minimum density of electromagnetic energy is required to provoke the rupture of a molecule by photochemical means.” I have pointed out that this reasoning is analogous to supposing that, to break up a molecule by electrochemical agency, a certain density of electrical energy would be necessary.The energy density is of little importance when we wish to break up a chemical compound; the volts alone play a part. In the same way frequency alone is concerned in photolytic rupture. In my memoir of April, 1911, I expressed that view in the following words : “The frequency of vibration plays the part of potential in a radiant system in the same way as temperature does in a thermal system and electrical potential in an electrified system. The notion of photochemical potential seems to be applicable to decomposition by light or PhotuQsis as simply as electrical potential is to el‘ectroZvsis. Every photolytic decomposition demands a ininimum phutuchemicad puteatial ; with ultra-violet radiations we obtain in a few hours a multitude of reactions that the electric arc or sunlight could not produce, however long their action be applied.” I have manya time restated this point of view, and I have demonstrated that the luminous frequency supplies a direct measure of the chemical affinity like the electro- niotive force.Thus I observed that the decomposition of hydriodic acid (in gas form), inappreciable in the red, is already noteworthy in the blue ; that the de- composition of gaseous hydrobromic acid, inappreciable in solar light, only commences in the ultra-violet (A < 0.3 p) ; and that finally the decomposi- tion of gaseous hydrochloric acid requires radiations from the extreme ultra-violet (A < 0 - 2 p). I found that this order of stability to light is the same as that to heat.Hydroiodic acid is indeed dissociated already at a dark red glow, hydrobromic acid about 700°, and hydrochloric acid only above I 5 00’. The same gradation is again observed with respect to electricity ; the electrolysis of hydroiodic acid requires 0’5 volt, that of hydrobromic acid 1.0 volt, that of hydrochloric acid 1.4 volt. Einstein further said in 191 z (Zot. d.) : ‘( One does not understand why radiations of high frequency can produce elementary phenomena of greater energy than radiations of lower frequency. We do not understand the specific effect of frequency any more than the absence of the effect of intensity. The difficulties which a satisfactory theory of these fundamental phenomena encounters appear at present insurmountable.” We have seen, on the contrary, how simple the interpretation of all these phenomena becomes when we are guided by the energetic conception which I have outlined.Ideas which are criticised as “strange, bizarre, incompreliensible ” (epithets we hear incessantly repeated with respect to the quantum theory) are simply ideas to which we are not accustomed. Combination of the above formulze shows that the same velocity z, may be communicated to a corpuscle of mass m by the action of a level differ- ence which may be electrical E, or thermal T or radiant N. Things do not take place in that way. ’‘ La ThCorie du Rayonnement et les Quanta,” p. 930.474 PHOTOCHEMICAL EQUIVALENCE 6: QUANTUM THEORY +nzv2 = eE = sT = hN. u = JzeE/m = J~zs‘l’lrn = ,/2hN/m. The temperature 1’ corresponds with the frequency N and the potential E. The idea that a definite frequency should correspond with every tem- perature has been suggested by many an author.But most of them made a given temperature correspond with the frequency of maximum energy in the spectrum of the black body. That is an artificial relation, much less well founded than the one I have proposed. As regards the correspondence between frequency N and potential E its importance for the study of X-rays and y-rays is well understood. If the parallelism to which I have drawn attention brings out the analogy of the laws governing electrical energy, thermal energy and radiant energy it estiblishes thst the thing which is common to all these formulz is the mass ?it of the negative constituent. From this point of view the term coy-uscde, first proposed by J.J. Thomson, was more happily chosen than the term edectron, which has since prevailed, but which only recalls one of the properties of the corpuscle, its electric charge e, whilst it excludes its charge of radiant entropy h and its charge of thermal entropy s. There correspond then to the atoms of matter three invariant atoms : e, s, h, the electron, the thermon, the radion. They represent the cap- acity atoms of electrical energy, of thermal energy, and of vibratory energy. In all these three cases the atom is independent of the nature of the body; that naturally suggests the idea of the unity of matter. The modern theories which see in each natural elementary unit or atom the juxtaposition of two electricities of opposite signs appear now in the light of a rejuvenescence of the old fluid theory which dominated the eighteenth century.They in- troduce us again to “Aepims atomised,” as Kelvin said in referring to the electron hypothesis in one of his last communications. After the atomised eZeeciric quid combined with the theory of electrons we are witnessing the resurrection of the atomised Zzminousfduid combined with the theory of quanta. One need not be a prophet to predict in the future development of science a similar good fortune to the atomised caZorz~k fluid combined with the thermon. If we wish to find a model helping us to visualise these conclusions, ac- cording to which the atom has the same capacity for all forms of energy whatever be the body considered, we might liken the atom to a small bottle containing the same quantity of electricity, of thermal entropy and of radiant entropy.But the abstract form of the language of energetics does not appeal to imagination. People have not hesitated, therefore, to materialise the atom of electricity, the electron, under the form of a small sphere capable of being eventually transformed into an ellipsoid. The radion, the quantum of Planck, is now being subjected to the same trans- formation ; wme people are already able to see it as a small billiard ball capable of colliding with an electron and of deflecting it while recoiling. Before long we shall find a similar imagery proposed for the thermon. All these little projectiles remind us moreover in a singular manner of the corpuscles of the emission theories of Epicurus and of Newton, which had almost gone out of fashion and which now Iuve once more come into marked favour : ‘( Midfa rennscel.ttur p a e jam ceciderc.)) THE LAW OF PHOTOCHEMICAL EQUIVALENCE AND THE PLACE OF THE QUANTUM THEORY IN RELATION TO THE ATOMIC THEORY AND ENERGETICS. BY PROFESSOR DANIEL BERTHELOT (PARIS). TRANSLATED BY H. BORNS. Communication received August 2 6th, I g 25. Within recent years the law of photochemical equivalence has received several confirmations and has been presented in some of these cases as exact, in others as grossly erroneous. The quantum theory has on the other hand been considered even by its most eminent protagonists as altogether revolutionary and as contrary to the classical principles of science.I believe the law of photochemical equivalence to hold rigorously, provided we define the conditions of its applications precisely. There is nothing new about these conditions which were precisely defined in 1865, as dominating the whole of photochemistry, by Marcellin Berthelot. On the other hand, I think that the fertility of the quantum theory, notably in chemistry, lies in the fact that it finds its place naturally in the classical frames of energetics and atomistics. I explained before the International Congress, held at Brussels in 191 I for the purpose of discussing the quantum theory, my view concerning these matters in an article, published on April 30, 191 I, in the Rev. Gin. des Siences, on “The Chemical Effects of Ultra-violet Rays,” and particu- larly in Part IV.of this article on “Thermodynamics of Ultra-violet Radiations : the Photochemical Potential.” That view is based on the distinction of the two factors (capacdty and tension) of the radiant energy, and on the novel conceptions of radiant entropr and of phtochmical potentiaZ, parallel to the classical conceptions of thermal entropy and of electrical potential. I developed these ideas in my paper on “Ultra-violet Radiations,” and subsequently in several notes presented to the AcadLmie des Siences; further in my communications to the Soc. ELanf. de Phys. (March I, 1912) on ‘‘ Photochemical Effects of Ultra-violet Rays,” and (March 5 , 1915) on “The Relation between Radiant Energy and other Forms of Energy ; ” in my memoir on “The Reciprocity of Electrical and Magnetic Phenomena ; the Elementary Discontinuous Factors of Energy ” ; I n my opinion matters are less complicated.1 Bull. SOC. Inglrt. Civils, Dec. 1911. 2’‘ The R61e of Wave-Length in Photochemical Reactions,’’ C.R., 1% 1597, 1912 ; ’@ Kinetics of Photochemical Reactions,” 160, 519, 1915. 3 Bull. SOC. Internat. Electr. 131 2, 53 and 55, 1916. 463464 PHOTOCHEMICAL EQUIVALENCE & QUANTUM THEORY in my paper on the “Chemical Aspect of the Quantum Theory and the Thermodynamics of Photochemical Reactions,” and on “ The Quantum Theory from the Chemical and Thermodynamical Standpoint.” The Two Factors of Radiant Energy, the Factor of Capacity (Radiant Entropy or Action), the Tension Factor (Vibratory Frequency or Photochemical Potential).According to the ideas of Rankine and Maxwell, developed particularly by Gibbs and H. le Chatelier, every form of energy may be represented as the product of two variables, one of position, the other of tension. The former may be called capacify factor (or extension factor) ; the other tension factor (or equilibrium factor or energetic potential). Form of Energy. Tension Factor. Capacity Factor. Superficial, AS. Surface tension, A. Surface, S. Volumic, PV. Pressure, P. Volume, V. Thermal, 02. Temperature, 0. Thermal entropy, 2. Electrical, EQ. Electromotive force, E. Quantity of electricity, Q. Radiant, NH. Frequency of vibration, N. Radiant entropy, H. Chemical, @M. Affinity (chemical potential), a. Number of molecules, M. The essential function of the tension factor is regulation of the equilibrium.In order that two systems be in equilibrium, they must have the same tension. This factor is independent of the mass of the systems. The capacity factor, on the other hand, is proportional to the mass of the system. Doubling the mass, means doubling its volume, its entropy, the quantity of electricity, etc. One of the direct consequences of this property is the following. When we have determined the numerical value of the energetic capacity of a system with respect to the gram-moZecuZe or mol. in accordance with actual chemical practice, it will suffice for the purpose of referring it to the true molecule and of obtaining the elementary value to divide the former value by 60.6 x 1 0 2 ~ (Avogadro’s number).In the table given above the two factors of the radiant energy are defined in accordance with the theory which I outlined in my paper of April, I g I I . I showed that my numerous photochemical experiments (published in the C.R.) enabled me to assign to the vibratory frequency the r61e of tension factor or of photochemical potential. As regards the second factor I proposed the name radiant entropy on account of its analogy to thermal entropy I showed in fact that the degradation of the radiant energy is governed by a principle analogous to the principle of Carnot. Just as the maximum work done by a heat engine operating between the temperatures T2 and T1 is equal to I - T1/T,, so the maximum work of a radiant machine operating between the frequencies N, and N, is equal to I - NJN,.This conception of the phenomena enables me at once to answer a question which Nernst and G. Lemoine have considered one of the most interesting of photochemistry, viz., which fraction of the radiant energy is utilisable, i.e., can be transformed into mechanical work ? The rale which Carnot’s principle assigns to temperature in the case of the heat engine is taken by trequency in the case of the radiant energy engine. These views have later been confirmed by Maurice and Louis de Broglie in their X-ray 1 Bull. SOC. Chimique de France [4], 35, 241-302, March, 1924. Bull. SOC. InKktt. Civils, May-June, 440-4789 1925.PROFESSOR DANIEL BERTHELOT 465 studies.' I t will be seen that the quantity which I call radiant entropy is nothing but the action of Hamilton and of Planck.The use of the term entropy has, in my opinion, the advantage that it indicates at once, by virtue of notions now classical and familiar, that the quantum conception marks a departure from rational mechanics as based upon reversibihty for the same reasons which render the Carnot principle irreconcilable with those of mechanics. The atomic structure of matter implies this statistical irreversibility which is expressed by the so-called law of large numbers. The Law of Photochemical Equivalence. Special Case of the Law of Equivalent Molecular Capacity. Physico-Chemical Significance of Planck's Constant : its analogy with Faraday 's Constant. The study of the capacity factors of different forms of energy shows that they obey the same physico-chemical law which (in my paper contributed to the Sac.Ikternat. EL!, I g I 6) I proposed to call the law of equivalent mode- cular capacities. According to this rule, whatever the form of energy in question, adl chmical units (molecular atoms) have the same energetic capacify indtyendent of the nature of the body. I n particular this proposition finds expression in the law of equivalent volumes ufgaseous bodies of Gay-Lussac, which is the basis of atomic nota- tion, and in the law of edectrochemicaZ epuivalente of Faraday. When a chemist writes an elementary equation such as : I vol. hydrogen + I vol. chlorine = z vol. HCl. z vol. hydrogen + I vol. oxygen = z vol. H,O. 3 vol. hydrogen + I vol. nitrogen = 2 vol. H,N, it is implied that there exists, for gaseous bodies, the same unit volume for hydrogen, oxygen, chlorine, nitrogen, etc.Referred to the gram-molecule at N.T.P., this volume is I 1,206 ~ r n . ~ I n the same way one valency-gram of any metal, K, Na, Ag, Cu, Au, etc., carries in electrolysis the same quantity of electricity-g6,500 coulombs. The quantum notion is nothing but the law of equivalent molecular capacity in a form applied to radiant energy. Photodysis or decomposition by light is parallel to electroZssis or decomposition by electricity ; a valency- gram there transports always the same quantity of radiant entropy (or of action, if that word be preferred), equal to 4 x I O - ~ erg-seconds. This quantity of entropy can be measured in a photolytic process just as the quantity of electricity is measured in an electrolysis.In order to study the electrolytic decomposition we gradually raise the electric tension at the terminals and we determine the minimum tension required for this purpose ; that is the tension at which the phenomenon is reversible. The energy ex- pended is equal to the product of this tension and of the quantity of electricity applied. Similarly to study the photolytic rupture we increase the radiant tension, i.e. the frequency, up to the moment when photolysis sets in. The energy ex- pended is equal to the product HN, the factors being frequency N and quantity of radiant entropy applied H. I have made a particularly careful study of the constants of one photo- lytic decomposition, that of the ketonic sugars and notably of levulose.2 At this tension the phenomenon is reversible.' C . R . Dec. 2, 1921. a A levulose actinometer, C.R. 156, 707, March 3, 1913.466 PHOTOCHEMICAL EQUIVALENCE &. QUANTUM THEORY The photolysis sets in exactly at wave-length 0*30p, corresponding to frequency N = 1 0 ~ ~ . In order to determine the radiant energy consumed, we have to estimate, by photometric and chemical measurements, the luminous energy of the mercury lamp used, the fraction of this energy which is of wave-length less than 0.30~ and the portion absorbed by the solution and concerned in the chemical transformation. Details of this research will be found in my paper sent to the Soc. Chim. mentioned above. The result is the following : The radiant energy required for the breaking- up of one vdency-gram is W = 4 x 1o12 ergs; the corresponding radiant entropy is H = W/N = 4 x I O - ~ erg x second.This number is the photolytic constant, analogous to the electrolytic constant 96,s 00 coulombs (9650 c.g.s. units). The figures so far given are referred to the gram-molecule; to refer them to the true molecule we have merely to divide them by 60.6 x 1022. The electric charge per gram equivalent being 9650, the elementary charge will be 1.59 x I O - ~ O c.g.s. unit. The gaseous volume per gram equivalent being 11,2c6 ~ m . ~ , the elementary volume will similarly be 1-85 x 10-20 ~ r n . ~ . I t follows from these considerations that combination and decomposition in gases take place in jumps by multiples of 1-85 x 10 - 2o C M . ~ at N.T.P. The phenomena will never be observed with smaller volume variations and the figure deduced really represents the elementary volume.Thus normal ebullition of a liquid consists of the jerky emission of small bubbles of vapour which at normal temperature and pressure would have the volume I -85 x z x I o - 20 ~ m . ~ The growth of the gaseous volume is discontinuous. Heating a liquid by an external source will not evolve any bubbles, not half or a quarter of a bubble until the energy supplied is sufficiently strong. Then one bubble is liberated, more energy is absorbed, more bubbles are evolved, and so on. Whatever the liquid evaporated, the volume of each elementary bubble is the same. The source of electricity sends energy in bundles or parcels to the electrodes; when the supply is sufficient, a first ion is detached which carries a quantity of electricity equal to 1-59 x 10 -20 ; a second ion cannot be liberated before a second parcel has arrived.As in the case of evaporation the elementary unit of energetic capacity, ie., in this instance the electric charge, is in- dependent of the nature of the body. Electrolytic decomposition takes place in similar jumps. The Law of Definite Proportions. Matter Imposes the Discon- tinuity of its Atomic Structure on the Capacity Factors of the Diverse Forms of Energy. All these discontinuities are a consequence of the fundamental discon- Chemical notation is based upon the law of definite The series of compounds tinuity of matter. proportions which is itself a discontinuity law. which two bodies, e.g., nitrogen and oxygen form : N@,, N01, NO,, Nos, Nod, NOS, is not a continuous curve, but a stairway of six steps. The discontinuity is particularly striking when we compare the gas volumes on the ground of the simple relations of Gay-Lussac.One volume of nitrogen combines with I, 2, 3 volumes of oxygen, but never with a fractional volume. I t is natural to assume that this chemical discontinuity, which is an expression of the atomic structure of matter, must be traceable in the physical laws.PROFESSOR DANIEL BERTHELOT 467 Long ago Marcellin Berthelot recognised that, when physics would descend down to the elements of matter, that is to the atoms as chemistry does, it would likewise have recourse not only to differential calculus, which is the science of continuity, but also to the processes and symbols of arithmetic, which is the science of discontinuity.We are at present witnessing this evolution in the quantum theory and its application to the lines of the spectrum. But, contrary to what is too frequently repeated, the theory of quanta does not upset our conceptioni of the natural laws: it is simply the form which the atomic discontinuity takes in the domain of vibratory energy. Matter h s a discontinuous structure and it imposes this discon tinuity, not upon energy itsell: as is often stated erroneously, but on th capacity factors by which the diverse forms of energy mangest thrnsehes. Since there are elements of matter or atoms, there are also elements of space, elements of electric charge, elements of surface, elements of thermal entropy and of radiant entropy.The mechanism of radiation by quanta as discovered by Planck does not in any way differ from the mechanism which we have outlined for evaporation and electrolysis. All these pheno- mena (evaporation, electrolysis, radiation) consist of a liberation in steps, not of atoms of energy, but of atoms of energy capacity. In the case of radiation, as in those of vaporisation and electrolysis, it is sufficient to divide by 60.6 x 1022 the number H = 4 x I - o - ~ erg-seconds, found above in the photolysis of a gram-molecule, in order to arrive at the quantum h = 6.55 x I O - ~ ~ erg x second, referred to the true molecule. From the historical standpoint it is curious to note that, in the cases of the elastic energy of gases and of electric energy, the quantum was first discovered as referred to the gram-equivalent, and that the hue quantum referred to the atom was deduced by dividing the value by 60-6 x 1 0 2 ~ .I n the case of the radiant energy the contrary applies. The true quan- tum referred to the atom (the Planck constant h = 6-55 x 10-2') was first found, but this by an accidental calculation, which was so unexpected that the Brussels Congress of 191 I discussed for a long time the meaning which it should attribute to this quantity without succeeding in defining it clearly. The illustrious president of the Congress, H. A. Lorentz, more- over, did not indulge in excessive illusions when he said in his inaugural address : " I shall admit that what we contribute to immediate progress does not amount to much.In fact this progress is due more to individual efforts than to the deliberations of the Congress." The constant of Planck, the meaning of which seemed so enigmatic to the members of the Brussels Congress, appears then to be the elementary photochemical constant, analogous to the elementary electrochemical con- stant of Faraday. Just as the latter is the atom of electricity or el'ecfron e = 1.59 x I O - ~ " so the former is the atom of radiantentropyh= 6-55 x 1 0 - 2 ? I have proposed to call this unit the radion. The term has the advantage over the term quantum of not being equivocal ; for owing to the confused ideas and the groping of which I have spoken the word quantum is used to designate sometimes an element of action, sometimes an element of energy, and there exists an infinity of quanta of energy whilst there is only one quantum of action.The physical meaning of the element of discontinuity h appeared mysterious for a long time. Ylanck saw first an element of energy in it and, if he was later induced to recognise it as an element of action, that was not done on account of some initial reasoning based upon468 PHOTOCHEMICAL EQUIVALENCE & QUANTUM THEORY the idea of an element of energy but, apart from all theoretical considerations, simply not to put himself in contradiction with the principle of Carnot. Lorentz remarked: “From the historical point of view the element of energy takes priority over the element of action.” I t is moreover well known that, just as the value of the electron as deduced from the chemical equivalent has subsequently been met with in a multitude of optical, magnetic and radioactive phenomena, etc., in the same way the value assigned to the radion by the law of photochemical equivalents reoccurs in measurements of radiation, specific heat, spectrum lines, photoelectricity etc.The Necessity of Excluding Spontaneous Irreversible Reactions in Verifications of the Law of Photochemical Equivalence. Before leaving this part of the subject it will be useful to say a few words concerning the objections to the validity of the law of photochemical equivalence raised on account of certain experimental discordances. The law may be enunciated in the following terms : In any reversible photo- chemical reaction, whatever be the compound in question, the breaking-up of a valency corresponds to the liberation of the same quantity of radiant entropy.Or again: The appearance (or disappearance) of a material chemical unit (molecule) is linked with the appearance (or disappearance) of a unit of energetic capacity, that is, a unit of radiant entropy (radion). That this may be so, the reaction must be reversible; that point I have already emphasised. I t is not otherwise in the case of Faraday’s law; that law can be verified, eg., by the decomposition or recomposition of water (in a voltameter or gas cell). We should, on the other hand, only arrive at illusory results in repeating the experiment with an irreversible reaction such as the decomposition of water oxygenated at ordinary temperature. Let us consider a photochemical reaction which was studied early in the nineteenth century by Berthollet, Gay-Lussac and ThCnard, the com- bination of hydrogen and chlorine.Exposure to ultra-violet radiation will start the reaction in this explosive mixture. The illumination acts like a trigger; there is a tendency to combination, but it is opposed by passive resistances. In this case there is no relation between the quantity of radiant entropy supplied by the ultra-violet radiation and the quantity of chemical compound formed. Now in 1865, Marcellin Berthelot pointed out that the whole of photo- chemistry is dominated by an essential distinction on which he has frequently insisted.’ The first are of the exothermic type and tend to arise spontaneously.(‘ The light,” he said, “here acts like a match which lights a bundle of firewood.” The second are of the endothermic type. They are reversible reactions; the light supplies the energy necessary to raise the chemical level. H e selected a few reactions (decomposition of nitric or of iodic acid by solar rays) in which the chemical work done by the light could accurately be estimated. These reactions are relatively rare in the range of visible light; but my studies in the ultra-violet have enabled me to multiply their numbers. The objections raised against the law of photochemical equivalence are in general There are two kinds of chemical action of light. 1 Revile des Cows publics, 1865 : Novel Researches in Thermochemistry ; Endo- Ann. de Chinz. 18, 83, thermic and Exothermic Reactions‘ ; Chemical Effects of Light.1869 ; Essai de MCcanique chimique, I. p. 20.PROFESSOR DANIEL BERTHELOT 469 due to a non-understanding of this fundamental distinction between irreversible spontaneous reactions and reversible reactions. lnsufficiency of Verifications of the Law of Photochemical Equi- valence based upon Heat of Reaction. More serious objections can be taken to the mode of calculation adopted in most of these verifications. I consider it useful clearly to put this point, for many authors do not even appear to suspect it. A correct calculation of the radiant entropy demands an exact evaluation, by photochemical and chemical means, of the radiant energy of the source and of the energy utilised in the chemical reaction, as well as of the photochemical potential of the reaction.The manner of the calculation has already been indicated. In the majority of cases support of the law of photochemical equivalence has, however, been based upon the use of a more rapid method which relies upon the heat of reaction, determined either directly in a calorimeter or even deduced from certain physico-chemical relations. These verifications lack convincing force. Sir William Thomson, it will be remembered, proposed to calculate the electromotive force of the Becquerel-Daniel1 cell and thus indirectly to confirm the law of Faraday thermochemically by starting from the heat of formation of zinc sulphate and of copper sulphate. His argument presumed that the whole chemical energy was transformed into electrical energy.But Gibbs showed subsequently that the calculation could only be accurate in cases where the two quantities E and E - 6E/6T could be substituted for one another, that is, if 6E/6'r = 0, and if the e.m.f. E were independent of the temperature T. From my note of March 5, 1 9 1 5 , ~ on the relations of radiant energy to other forms of energy, in which I gave the thermodynamical equations governing actino-capillarity and actino- electricity, etc., it follows that verifications of the law of photochemical equivalence relying upon heat of reaction could similarly be accurate only in cases where N and N - T6N/GT had the same value, i.e., if the photo- chemical potential N were independent of the temperature. But up to the present no sufficient attempt has, so far as I am aware, been made to take measurements in this sense; the verifications made must hence be regarded as mere approximations.The Three Fundamental Categories of Physical Magnitudes : Mechanical, Thermal, Electrical, and the three Corresponding Invariants of Capacity : Radion, Thermon, Electron. To complete this study I have to indicate which of the elementary dis- continuous factors of capacity of the diverse forms of energy possess the character of physical invariants. The element of gaseous volume V = 1-85 x 1 0 - 2 ~ ~ m . ~ is not of that nature, since it depends upon temperature and pressure. The equation of perfect gases PV = RT shows that the in- variant is the function PV/T, or R, which has the dimensions of entropy. Now in his classical paper of 1888 on Chemical Equilibria, H. Le Chatelier first pointed out tEat the thermal dissociations of various chemical systems yield fairly the same numerical values for the quotient L/T, that is, for the variation of thermal entropy (L being the latent heat of reaction and T the temperature).This demonstration helps us to recognise that the law of equivalent molecular capacities is applicable to thermal energy and that there is a law of thermochemical equivalence in analogy to the law of 1 SOC. Franc. Phyt. 31470 PHOTOCHEMICAL EQUIVALENCE & QUANTUM THEORY electrochemical and photochemical equivalence. The dissociation by heat or thermolysis is analogous to the dissociation by electricity or electrolysis and to the dissociation by light or photolysis.Every thermolysis liberates per valency-gram the same quantity of thermal entropy independent of the nature of the body. This quantity of radiant entropy is, as I have shown in previous publications, equal to + R when referred to the gram-molecule. I t represents, therefore, the calorific capacity of a monatomic gas, uiz. 2.98 cal. per deg., or, in mechanical units, 1-247 x IO* erg. per deg. By dividing this number by 60.6 x 1 0 ~ ~ we find the elementary quantum or the atom of ther?naZ entrojy, s = 2-06 x erg. per deg. For this atom s I have proposed the name Thermon on account of its analogy to the atom of electricity or electron e, and the atom of radiant entropy or radion h. I t is very remarkable that the same invariant s recurs in thermal phenomena.I showed in 1916 that the law of equivalent molecular capacity holds for the surface energy orkapillary energy, provided we do not consider a capillary membrane in the presence of the generating liquid- in which case the capillary tension A would depend upon temperature alone and be independent of the surface in the same way as the pressure of a saturated vapour is independent of the volume-but assume the whole liquid Ito be spread in a thin capillary coating (a monomolecular layer). Under those conditions, A representing the capillary tension, S the surface of the membrane, T the temperature and T, the critical temperature, the fluid conforms to the following simple formula, the characteristic equation ofthe cajiZZaryphase which is analogous to the equation of a perfect gas, AS = $ R(T, - T).I n this state of the monomolecular layer and under comparable conditions (equal surface tensions and equal departures from the critical points) a gram-molecule of any liquid whatever occupies the same surface. Thus we may speak of equivalence in surface in analogy to the equivadence in volume of Gay-Lussac, the eZectrochemicaZ equivadence of Faraday, and the photo- chemicaZ equivaZence of Planck and of Xinstein. We then find for the capacity factor of the capillary energy (that is to say, for the surface) a natural elementary unit ; but this unit varies with the temperature and the surface tension. Yet this constant K does not introduce a new invariant, since K = +r = $s. There are definitively only three variants: s, e, h. Each of these three invari- ants is characteristic of one of the great categories into which all physical magnitudes (mechanical, thermal, electric) may be classified from the stand- point of energetics.The mechanical magnitudes may be expressed as functions of three fundamental magnitudes. I t is customary to select length L, mass M and time T ; but three others, e.g., length, velocity, and force, might equally well be chosen. Thermal magnitudes cannot be expressed as functions of three mechanical magnitudes such as L, M, T. A further magnitude, of purely thermal character, is needed. The one generally selected is the temperature ; but some other thermal magnitude, e.g., entropy, might be adopted. Similarly electrical magnitudes cannot simply be expressed in terms of L, M, T.A fourth magnitude, electric or magnetic, is required ; preference is given either to the di-electric constant or to magnetic permeability. Of the three invariants e, s, h, the first falls into the category of the electrical magnitude, the second into the thermal, and the third into the mechanical magnitudes. These are the three capacity invariants of the The invariant function is AS/(T, - T) = K.PROFESSOR DANIEL BERTHELOT 471 electrical, thermal and vibratoiy energies. The three invariants are funda- mental and independent of one another; not one of them is reducible to the other two. It is noteworthy thst the theory of relativity which has led to a modification, in moving systems, of the magnitudes which were habitu- ally regarded as primordial, such as length or time, does not assail the invariance of e, s, A.I f the old mechanical ideas have not emerged quite intact out of the struggle with the novel conceptions, the old energetic conceptions have successfully resisted all attacks. The fact that the invariant h can be expressed as a function of the mechanical magnitudes L, M, T, induces us to reject the opinions which Lorentz and Planck gave expression at the Brussels Congress.’ Lorentz remarked : ‘< Too great importance should not be attached to the circumstance that h has the dimensions of action. The A has also the dimensions e2/V if e signifies an electric charge measured in electrostatic units. I f we replaced h by e2/V in the formula for the black radiation, we might have to think that the universal element which we are searching for should be, not a certain action, but a certain electric charge,” and Planck replied : ‘‘ I can on principle only concede this point. I t is possible that we may have to connect h with e and with V, or conversely e with h and with V.” Once we admit that A is the capacity factor of vibratory energy, expressed in terms of L, M, T, it is clear that h is of purely mechanical character and independent of all electrical magnitudes.I t may play a part not only in the phenomena of radiation but in other vibratory phenomena purely mechanical. The only restrictions to be imposed is that the phenomena be periodical and characterised by a frequency N, because it is this frequency which represents the tension factor of energy of which A is the capacity factor. We are therefore unable to give our signature to the opinion which Planck expressed at the Congress (p.113) : “There is no doubt that inas- much as the hypothesis of quanta possesses a profound meaning, the element of action A must have a fundamental importance also for non- periodical phenomena, as Sommerfeld has already shown.’ ’ Kinetics of Electrochemical, Thermochemical, and Photochemical Reactions. The knowledge of the values of e, s, h enables us to solve important problems of molecular kinetics and to demonstrate (as I showed in ‘‘ Cin& tiques des Reactions Photochimiques,” C.X. 160, 519, 1915) that the velocities which particles acquire, in mechanical, thermal, and radiant phenomena, under the influence of a difference in energetic level present a mutual remarkable parallelism.In elementary mechanics, a point of mass m and weight p raised to the level Z possesses the quantity pZ of potential energy. In free fall through a vacuum it acquires the kinetic energy +mu2, so that &mv2 = pZ and v = JzpZ/m. I n that expression p represents the capacity factor of gravity energy, the level Z represents the tension factor, and p/m the gravitational acceleration at the level considered, which is independent of the body. Under the influence of a sufficient potential difference the molecule is split into a part negatively electrified of mass m and electric charge e (corpuscle of J. J. Thomson) and a positive nucleus of mass M and electric charge - e. The electric charge one and the same for all bodies, is equal to 1-59 x I C - 2 0 ; Formulz of the same type result for the diverse forms of energy.1 ‘‘ Thkorie du Rayonnement et les Quanta,” p. 131.4 7 2 PHOTOCHEMlCAL EQUWALENCE & QUANTUM THEOR the mass of the corpuscle, likewise the same for all bodies, is equal to omgo x I O - ~ ~ . When we accept this for the vacuum tube, the electric decomposition will be accompanied by projections from the electrodes in opposite directions of corpuscles and nuclei. Under the influence of the potential difference E the corpuscles are expelled with a force such that +mv2 = eE; v -- J2eElm; for a p.d. of 40,000 volts the velocity would be about 120,000 km/sec. hor the positive nuclei of mass M, the relations are +Mu2 = eE ; ZI = J Z / M ; in the case of the hydrogen nucleus, e.g., whose mass is 1850 times that of the corpuscle, the velocity, at 40,000 volts, would be 2 7 70 km/sec.A sufficient rise T in tem- perature splits the chemical molecule into two portions, a negative corpuscle of mass nt which, in a vacuum, would acquire a velocity such that mv2 = sT and v = J2sT/m, and a positive nucleus of mass M, the rela- tions being 3Mv2 = sT and 77 = ,/2sT/M. The quantity s = 2.06 x I 0-16 (the atom of thermal entropy) is independent of the nature of the body just as is e, the atom of electricity. Application of these formulz to hydrogen, for which M = 2-016/60*6 x I O ~ ~ , show that at the temperature of melt- ing ice (T = 273-1') the hydrogen nucleus would acquire a velocity of 1830 m/sec. which is sensibly the velocity which the kinetic theory ascribes to the hydrogen molecule.But apart from the movement of the nucleus we have also to consider the velocity of the corpuscle ; that velocity already calculated is the same for all bodies. The co-existence, in the usual phenomena of thermal agitation, of two different velocities, the one belonging to the nucleus the other to the corpuscle, manifests itself in the absorption spectra by the simultaneous presence of two characteristic conjugated bands, the one in the ultra-violet, ascribed to the corpuscle, the other in the infra-red attributable to the nucleus. The dissociation by heat or thermolysis is hence effected by a mechanism analogous to electrolysis or photolysis. The decomposition of a molecule, or the rupture of a valency, if that mode of expression be preferred, is accompanied by the consumption of an elementary unit of energetic capacity, independent of the nature of the body.The thermal dissociation, like the other dissociations, consists in the rupture of a valency and the splitting of a molecule into a negative corpuscle and a positive nucleus. One cannot, therefore, say that the term photo-electricity is particularly well chosen. The word seems to imply that the dissociating action of the light is exercised upon bodies by a mechanism peculiar to light. That is not so. The dissociating effects of heat and of electrolysis are enacted by the same mechanism. The chemical conception of valency appears to be inseparable from the conception of the electrical constitution of matter.The chemical forces are nothing but the old electrical forces of Berzelius. From the formuke deduced it results that, whatever the mode of energy, the velocity of the particles is equal to the square root of the double product of the tension and capacity factors, referred to unit mass. The theory of radiant energy above outlined, according to which the tension factor is the frequency N and the capacity factor is the radiant entropy h, indicates in tne same way that a particle of mass m having a charge h of radiant entropy, carries when brought up to the energetic level N a quantity of energy hN which, manifested in kinetic form, imparts to the particle a velocity v such that, in a vacuum,.+mv2 = h N , ZJ = JzhN/m. We arrive thus in a simple way at the energetic magnitudes of Einstein's photo-electric formula.As in the case of electricity and heat we should, moreover, give the analogous formula for the positive nucleus, into which the mass M would enter; but we have no experimental data regarding that point. I t is ~- - Let us now examine dissociation by heat.PROFESSOR DANIEL RERTHELOT 473 known that the velocities calculated are superior to those which the particles acquire under the available temperature gradients. Twenty years ago Gustave le Bon emphasised in his studies of the dissociation of matter and its transformation into energy that the dissociating effect of light is incomparably stronger than that of heat. The results mentioned, although confirmed by experiment, have often been considered very surprising.‘‘ They were not at all what was expected on the ordinary theories,” Einstein wrote in 1 9 ~ 2 , ~ “one would think that a certain minimum density of electromagnetic energy is required to provoke the rupture of a molecule by photochemical means.” I have pointed out that this reasoning is analogous to supposing that, to break up a molecule by electrochemical agency, a certain density of electrical energy would be necessary. The energy density is of little importance when we wish to break up a chemical compound; the volts alone play a part. In the same way frequency alone is concerned in photolytic rupture. In my memoir of April, 1911, I expressed that view in the following words : “The frequency of vibration plays the part of potential in a radiant system in the same way as temperature does in a thermal system and electrical potential in an electrified system.The notion of photochemical potential seems to be applicable to decomposition by light or PhotuQsis as simply as electrical potential is to el‘ectroZvsis. Every photolytic decomposition demands a ininimum phutuchemicad puteatial ; with ultra-violet radiations we obtain in a few hours a multitude of reactions that the electric arc or sunlight could not produce, however long their action be applied.” I have manya time restated this point of view, and I have demonstrated that the luminous frequency supplies a direct measure of the chemical affinity like the electro- niotive force. Thus I observed that the decomposition of hydriodic acid (in gas form), inappreciable in the red, is already noteworthy in the blue ; that the de- composition of gaseous hydrobromic acid, inappreciable in solar light, only commences in the ultra-violet (A < 0.3 p) ; and that finally the decomposi- tion of gaseous hydrochloric acid requires radiations from the extreme ultra-violet (A < 0 - 2 p).I found that this order of stability to light is the same as that to heat. Hydroiodic acid is indeed dissociated already at a dark red glow, hydrobromic acid about 700°, and hydrochloric acid only above I 5 00’. The same gradation is again observed with respect to electricity ; the electrolysis of hydroiodic acid requires 0’5 volt, that of hydrobromic acid 1.0 volt, that of hydrochloric acid 1.4 volt. Einstein further said in 191 z (Zot. d.) : ‘( One does not understand why radiations of high frequency can produce elementary phenomena of greater energy than radiations of lower frequency.We do not understand the specific effect of frequency any more than the absence of the effect of intensity. The difficulties which a satisfactory theory of these fundamental phenomena encounters appear at present insurmountable.” We have seen, on the contrary, how simple the interpretation of all these phenomena becomes when we are guided by the energetic conception which I have outlined. Ideas which are criticised as “strange, bizarre, incompreliensible ” (epithets we hear incessantly repeated with respect to the quantum theory) are simply ideas to which we are not accustomed. Combination of the above formulze shows that the same velocity z, may be communicated to a corpuscle of mass m by the action of a level differ- ence which may be electrical E, or thermal T or radiant N. Things do not take place in that way. ’‘ La ThCorie du Rayonnement et les Quanta,” p. 930.474 PHOTOCHEMICAL EQUIVALENCE 6: QUANTUM THEORY +nzv2 = eE = sT = hN. u = JzeE/m = J~zs‘l’lrn = ,/2hN/m. The temperature 1’ corresponds with the frequency N and the potential E. The idea that a definite frequency should correspond with every tem- perature has been suggested by many an author. But most of them made a given temperature correspond with the frequency of maximum energy in the spectrum of the black body. That is an artificial relation, much less well founded than the one I have proposed. As regards the correspondence between frequency N and potential E its importance for the study of X-rays and y-rays is well understood. If the parallelism to which I have drawn attention brings out the analogy of the laws governing electrical energy, thermal energy and radiant energy it estiblishes thst the thing which is common to all these formulz is the mass ?it of the negative constituent. From this point of view the term coy-uscde, first proposed by J. J. Thomson, was more happily chosen than the term edectron, which has since prevailed, but which only recalls one of the properties of the corpuscle, its electric charge e, whilst it excludes its charge of radiant entropy h and its charge of thermal entropy s. There correspond then to the atoms of matter three invariant atoms : e, s, h, the electron, the thermon, the radion. They represent the cap- acity atoms of electrical energy, of thermal energy, and of vibratory energy. In all these three cases the atom is independent of the nature of the body; that naturally suggests the idea of the unity of matter. The modern theories which see in each natural elementary unit or atom the juxtaposition of two electricities of opposite signs appear now in the light of a rejuvenescence of the old fluid theory which dominated the eighteenth century. They in- troduce us again to “Aepims atomised,” as Kelvin said in referring to the electron hypothesis in one of his last communications. After the atomised eZeeciric quid combined with the theory of electrons we are witnessing the resurrection of the atomised Zzminousfduid combined with the theory of quanta. One need not be a prophet to predict in the future development of science a similar good fortune to the atomised caZorz~k fluid combined with the thermon. If we wish to find a model helping us to visualise these conclusions, ac- cording to which the atom has the same capacity for all forms of energy whatever be the body considered, we might liken the atom to a small bottle containing the same quantity of electricity, of thermal entropy and of radiant entropy. But the abstract form of the language of energetics does not appeal to imagination. People have not hesitated, therefore, to materialise the atom of electricity, the electron, under the form of a small sphere capable of being eventually transformed into an ellipsoid. The radion, the quantum of Planck, is now being subjected to the same trans- formation ; wme people are already able to see it as a small billiard ball capable of colliding with an electron and of deflecting it while recoiling. Before long we shall find a similar imagery proposed for the thermon. All these little projectiles remind us moreover in a singular manner of the corpuscles of the emission theories of Epicurus and of Newton, which had almost gone out of fashion and which now Iuve once more come into marked favour : ‘( Midfa rennscel.ttur p a e jam ceciderc. ))

ISSN:0014-7672    

DOI:10.1039/TF9262100463

出版商:RSC    

年代:1926

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. RELATIONS BETWEEN THE VELOCITY OF PHOTOCHEMICAL REACTIONS AND WAVE-LENGTH. 604PP 1 593P 20.9 18.0 0.229 0.223 BY PROFESSOR P. LASAREFF (Moscow). Communication received September 2 9th, I 9 2 5. 573PP 11'1 0.132 I n former papers,' I have demonstrated that the velocity of photochemical reactions is proportional to the absorbed energy and independent of the wave-length of the activating light. This law has been further studied by Bruner,2 Henri and Wurmser and the results of the investigations of these authors have confirmed my conclusions.AC C - E { A ~ ~ ~ : ~ ~ } 0'2 0'1 11.8 0 4 8 I2 16 20 FIG. I. In the present note, I give an account of experiments I have made, The results are shown in Table I. and Fig. I. using the same method and with the same substances as before. TABLE I. C is the concentration. 5 5 4 w 4'77 0'457 1 P. Lasareff, Anti. d. Physik. 24, p. 661, 1907;.9, p. 812, 1911. 2 L. Bruner, Sitrungber, der Krakarrer Akademze, p. 555, 1910. 3 V. Henri et R. Wurmser, yourrial de physique, p. 162, 1913. 475476 PHOTOCHEMICAL REACTIONS AND IVAVE-LENGTH A 642w 617PP ~04PuE.c 593PP 0'129 0.099 o - ~ o g 0.124 */hE 0'200 c.160 0.182 0.208 AC /E c/ C Einstein proposed the law which affirms that if an equal number of quanta of different light is absorbed by the substance the action is the same.The quantum of the activating light is equal to Q = hv (h is Planck's con- stant and vthe frequency). As v = - (v is velocity of light) we obtain the x Zr S73Pl-4 S54PP o-IIQ 0.096 0206 0'173 quanta by dividing E by hv and therefore the relative quanta will be equal to EX. give the values of ACi E and ,/XE. Acl C c number of absorbed number of absorbed I n Table 11. we TABLE 11. RELATIONS BETWEEN THE VELOCITY OF PHOTOCHEMICAL REACTIONS AND WAVE-LENGTH. 604PP 1 593P 20.9 18.0 0.229 0.223 BY PROFESSOR P. LASAREFF (Moscow). Communication received September 2 9th, I 9 2 5. 573PP 11'1 0.132 I n former papers,' I have demonstrated that the velocity of photochemical reactions is proportional to the absorbed energy and independent of the wave-length of the activating light.This law has been further studied by Bruner,2 Henri and Wurmser and the results of the investigations of these authors have confirmed my conclusions. AC C - E { A ~ ~ ~ : ~ ~ } 0'2 0'1 11.8 0 4 8 I2 16 20 FIG. I. In the present note, I give an account of experiments I have made, The results are shown in Table I. and Fig. I. using the same method and with the same substances as before. TABLE I. C is the concentration. 5 5 4 w 4'77 0'457 1 P. Lasareff, Anti. d. Physik. 24, p. 661, 1907;.9, p. 812, 1911. 2 L. Bruner, Sitrungber, der Krakarrer Akademze, p. 555, 1910. 3 V. Henri et R. Wurmser, yourrial de physique, p. 162, 1913. 475476 PHOTOCHEMICAL REACTIONS AND IVAVE-LENGTH A 642w 617PP ~04PuE.c 593PP 0'129 0.099 o - ~ o g 0.124 */hE 0'200 c.160 0.182 0.208 AC /E c/ C Einstein proposed the law which affirms that if an equal number of quanta of different light is absorbed by the substance the action is the same. The quantum of the activating light is equal to Q = hv (h is Planck's con- stant and vthe frequency). As v = - (v is velocity of light) we obtain the x Zr S73Pl-4 S54PP o-IIQ 0.096 0206 0'173 quanta by dividing E by hv and therefore the relative quanta will be equal to EX. give the values of ACi E and ,/XE. Acl C c number of absorbed number of absorbed I n Table 11. we TABLE 11.

ISSN:0014-7672    

DOI:10.1039/TF9262100475

出版商:RSC    

年代:1926

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. TRANSFORMATION OF ATOMS INTO RADIATION. BY PROFESSOR OTTO STERN (HAMBURG). TRANSLATED BY H. BORNS. The stellar theory of Eddington leads to the conclusion that a star loses a considerable portion of its mass during its evolution by radiation, ie., that matter is transformed into radiation and is ‘‘ radiated away.” Accept- ance of this hypothesis implies that we concede the existence of the inverse process, the transformation of radiation into matter.On that view a hollow radiating space would only then be in equilibrium when it contains a definite quantity of matter such that the portion of matter radiated away in unit time is equal to the amount of matter being formed from radiation. I t is tempting to assume that cosmic space is in this state of equilibrium. I made an attempt recently to calculate this equilibrium theoretically. I had recourse to semi-permeable membranes; that appeared too bold a step to some of my colleagues. To-day I shall therefore endeavour to dis- pense with semi-permeable walls in my deductions. I substitute the assumption that the energy and the entropy of a hollow space, which con- tains black radiation and an ideal gas in equilibrium, represent the sum of the values that these quantities would possess if gas and radiation were each alone present. The following symbols are used :- U total energy, S total entropy, V volume of the hollow space.m mass, fig energy, so entropy of a gas atom. 21, energy, s, entropy of a cm.y of black radiation. K Boltzmann’s cpnstant, h Planck’s constant. T absolute temperature. n number of gas atoms, c velocity of light. 21, = ZkT -I= u0, sg = Ad V/n + 3 . klT 4- so, where uo and so are the constants for zero values. Our assumption is then : p , gas pressure, p , radiation pressure. u = ?ZZCg + Vu,; s = nsg + vs,. The Gibbs’ condition of equilibrium is that the entropy is a maximum for constant energy and constant volume, i.e., when a gas atom is formed Paper read before the Bunsen Gesellschaft this year, to be published in the 2eits.f.E lektrochemic. 477478 TRANSFORMATION OF ATOMS INTO RADIATION from radiation (or vice versa) the entropy change involved must be- 6s = 0. provided that at the same time, Hence Since 6u, = Ti%,, we have- 6U = o and 6V = 0. 6U = u, + n6ug + V6u, = 0 6s = sg + n6sg + V6Sg = 0. 6U - T6S = U, - TJ, + n(&&, - Th,) = 0. ' + -.-6T, 3 k Since further 6u, = 3 K6T and 6s, = - - n 2T and therefore 8ug - T8sg = KT/n, the equilibrium condition is- U, - Tsg + KT = 0. The corresponding radiation expression being- u, - Ts, +$, = 21, - T 5 5 + us = 0, 3 7 - 3 the above condition of equilibrium may directly be deduced from the postulate that, at equilibrium, the " thermodynamic potentials " of gas and radiation must be equal to one another. If we desire to substitute the values for ug and sg into this equation, we have to express u0 and so in such a way that the zero level, to which energy and entropy are referred, is the same for gas and radiation.The resulting value for the energy is simply uo = m8.1 I n case of the entropy we take so = gk + kZ(2Tmk)3/h3,2 the accepted value for the entropy constant of an ideal gas. In the deduction of this value the zero condition assumed is that of the solid substance at T = 0. When we introduce this value of so we assert at the same time that within the range T = o the transformation of solid matter into radiation takes place without any change of entropy, i.e., we presume the validity of Nernst's theorem also for this case.On this supposition our condition of equilibrium yields after substitution of the values deduced for ug and sg and for uo and so, for the number of atom per cm.S the value- mcZ s0-5 -'% -- 72/V = e Te kT = (2rmT) e "1 h3. As regards electrons of mass 172, one ~ m . ~ would then contain one electron at a temperature of I 00 million degrees, and one molecule of electrons at 5 00 million degrees. I have discussed the difficulties resulting as to the high temperatures and especially as to the electronic neutrality of the universe in the discourse mentioned (Zoc. cit.). I will not discuss this point further on the present occasion, since I have not yet found any really satisfactory way out of this difficulty. But I should like to point out that my deduction is, owing to my stipulations respecting S and U, valid only as long as the density of the gas is low.Under other conditions the mutual reaction between matter and radiation (the dielectric constant) would have to be taken into con- sideration. If acy zero energy is to be ascribed to the radiation (Nernst) this ntca should be This would lower Eventually + kln (see Bunsen Ges. paper Eor. cit.). diminished by the value of this transformed energy at absolute zero. the temperatures calculated below. TRANSFORMATION OF ATOMS INTO RADIATION. BY PROFESSOR OTTO STERN (HAMBURG). TRANSLATED BY H. BORNS. The stellar theory of Eddington leads to the conclusion that a star loses a considerable portion of its mass during its evolution by radiation, ie., that matter is transformed into radiation and is ‘‘ radiated away.” Accept- ance of this hypothesis implies that we concede the existence of the inverse process, the transformation of radiation into matter.On that view a hollow radiating space would only then be in equilibrium when it contains a definite quantity of matter such that the portion of matter radiated away in unit time is equal to the amount of matter being formed from radiation. I t is tempting to assume that cosmic space is in this state of equilibrium. I made an attempt recently to calculate this equilibrium theoretically. I had recourse to semi-permeable membranes; that appeared too bold a step to some of my colleagues. To-day I shall therefore endeavour to dis- pense with semi-permeable walls in my deductions. I substitute the assumption that the energy and the entropy of a hollow space, which con- tains black radiation and an ideal gas in equilibrium, represent the sum of the values that these quantities would possess if gas and radiation were each alone present.The following symbols are used :- U total energy, S total entropy, V volume of the hollow space. m mass, fig energy, so entropy of a gas atom. 21, energy, s, entropy of a cm.y of black radiation. K Boltzmann’s cpnstant, h Planck’s constant. T absolute temperature. n number of gas atoms, c velocity of light. 21, = ZkT -I= u0, sg = Ad V/n + 3 . klT 4- so, where uo and so are the constants for zero values. Our assumption is then : p , gas pressure, p , radiation pressure. u = ?ZZCg + Vu,; s = nsg + vs,. The Gibbs’ condition of equilibrium is that the entropy is a maximum for constant energy and constant volume, i.e., when a gas atom is formed Paper read before the Bunsen Gesellschaft this year, to be published in the 2eits.f.E lektrochemic. 477478 TRANSFORMATION OF ATOMS INTO RADIATION from radiation (or vice versa) the entropy change involved must be- 6s = 0. provided that at the same time, Hence Since 6u, = Ti%,, we have- 6U = o and 6V = 0. 6U = u, + n6ug + V6u, = 0 6s = sg + n6sg + V6Sg = 0. 6U - T6S = U, - TJ, + n(&&, - Th,) = 0. ' + -.-6T, 3 k Since further 6u, = 3 K6T and 6s, = - - n 2T and therefore 8ug - T8sg = KT/n, the equilibrium condition is- U, - Tsg + KT = 0. The corresponding radiation expression being- u, - Ts, +$, = 21, - T 5 5 + us = 0, 3 7 - 3 the above condition of equilibrium may directly be deduced from the postulate that, at equilibrium, the " thermodynamic potentials " of gas and radiation must be equal to one another.If we desire to substitute the values for ug and sg into this equation, we have to express u0 and so in such a way that the zero level, to which energy and entropy are referred, is the same for gas and radiation. The resulting value for the energy is simply uo = m8.1 I n case of the entropy we take so = gk + kZ(2Tmk)3/h3,2 the accepted value for the entropy constant of an ideal gas. In the deduction of this value the zero condition assumed is that of the solid substance at T = 0. When we introduce this value of so we assert at the same time that within the range T = o the transformation of solid matter into radiation takes place without any change of entropy, i.e., we presume the validity of Nernst's theorem also for this case.On this supposition our condition of equilibrium yields after substitution of the values deduced for ug and sg and for uo and so, for the number of atom per cm.S the value- mcZ s0-5 -'% -- 72/V = e Te kT = (2rmT) e "1 h3. As regards electrons of mass 172, one ~ m . ~ would then contain one electron at a temperature of I 00 million degrees, and one molecule of electrons at 5 00 million degrees. I have discussed the difficulties resulting as to the high temperatures and especially as to the electronic neutrality of the universe in the discourse mentioned (Zoc. cit.). I will not discuss this point further on the present occasion, since I have not yet found any really satisfactory way out of this difficulty. But I should like to point out that my deduction is, owing to my stipulations respecting S and U, valid only as long as the density of the gas is low. Under other conditions the mutual reaction between matter and radiation (the dielectric constant) would have to be taken into con- sideration. If acy zero energy is to be ascribed to the radiation (Nernst) this ntca should be This would lower Eventually + kln (see Bunsen Ges. paper Eor. cit.). diminished by the value of this transformed energy at absolute zero. the temperatures calculated below.

ISSN:0014-7672    

DOI:10.1039/TF9262100477

出版商:RSC    

年代:1926

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. FLAME SPECTRA AND CHEMICAL REACTION. BY MISS C. E. BLEEKER (UTRECHT).~ Communication received August 2 I st, I 9 z 5 . Measurements on the relative intensities of several members of the first and second subordinate series in the flame spectra of the elements rubidium and caesium have previously been published.2 The experiments have shown that the ratio of these intensities depends neither on the concentration of the salt in the flame, nor on its temperature. Also, for this kind of excitation the ratio of the doublets is found to be The change in the successive intensities of lines in a series due to tem- perature variation in the case of thermal excitation may be estimated in the following manner.If T represents the temperature, K the Boltzmann con- stant, e the energy and p the statistical weight of the level under considera- tion, then the number of atoms which are in the state 4,3 for the case of temperature equilibrium, may be represented by : 2 : I. while represents this number for the 5 state. number of possible transitions is given by : I f W , and W, represent the transition probabilities, then the ratio of the The ratio W, : W, is generally supposed to be independent of the tem- perature, and we find for the ratio of the transitions : where hC b = - k' It follows that the variation of this ratio, if we consider two temperatures TI and T,, is given by the formula : - b(v1 - V.) - - - e (TI, TI,) 1 Communicated by Professor L.S. Ornstein. 2 2. fiir Physik, 1924, Bd: 27, 195. 9 The notation of Fowler is used. 4 79480 FLAME SPECTRA AND CHEMICAL REACTION Now for the oxygen flame we may put T = 2700' and for an ordinary For the case of caesium, the variation of the ratio : bunsen T = I 700'. can be expected. The above-men tioned measurements have been extended to potassium and sodium, and far these alkalis also analogous results have been obtained. The measurements were much more complicated as the lines are situated in less favourable regions of the spectrum and therefore the results show much larger mutual deviation than was the case for the heavier alkalis. As the temperature has no influence on the ratio of the intensities, it is impossible for the subordinate series found in flames to be caused by ther- mal excitation alone.The experiment of Haber,l which shows the emis- sion of the D lines of sodium due only to chemical binding of Na with C1, suggests that in the case offlames also, chemical reaction plays a part. I n our case, it is possible that besides temperature-radiation, the oxidation of alkali atoms is the cause of the emission of spectral lines. Wecan imagine the process in the following way. All the x-levels can be formed by black body radiation from the a-level, which is the normal state of the unexcited atom. 'The simplest way of excitation of the other (T- and &levels, is by absorption through atoms in the first x state. The number of atoms in this state, however, is very small, afortiort' the number of atoms which have an electron in the higher U- and &orbits is still smaller.The ratio of the lines due to emission from those levels would, for the case under considera- tion, depend on the temperature but the lines will be very faint. Let us now consider the second cause. The Cs atoms can be oxidised to Cs,O, the specific heat of oxidation being 83-99 cal. (Landolt) or to Csa02, with oxidation-heat of 142 cal. In both cases the energy set free in the reaction can be used for the ionisation of an Cs-atom, the ionisation energy amounting to 88 cal. The latter process can be performed by radi- ation or by collisions of the second kind. The ionised atoms will emit radiation, and the distribution of the intensities of the different emission lines will be proportional to the apriuri probability of the respective levels and the transition probabilities.Therefore, the total intensity of each line is composed of two parts, one due to thermal excitation and the other to the oxidation process. For the lines of the subordinate series the oxidation process prevails, and this can give us an explanation of the fact that the temperature effect cannot be found. The lines of the principal series, however, are much stronger than those of the subordinate series. I n their emission the oxidation process plays only a subordinate part. Within the limits of experimental error they will possess the intensity given by Planck's law, as has been shown by measurements on the temperature of flames made with the resonance lines. In order to consider the same question in the case of the other alkalis, we give the following table (see p.481). The table shows that in the case of the alkalis K and Na, the maximum value of the oxidation heat for the simple oxide is not high enough for total ionisation. For K the ionised state can still nearly be reached; in the case of Na,O, the oxidation heat is far less than the ionisation energy. For this alkali only the energy corresponding to the frequency @$ v,, is available, where v,, = 41449 represents the frequency of the normal state. The frequency under consideration amounts to 35426. Therefore the The experimental results do not show any variation. 1 Z. fur Physik, 1922, Bd. IX., 302.MISS C. E. BLEEKER Alkali Metal. L i . . . . N a . . . .K . . . . Rb. . . . c s . . . . Ionisation-Energy. 123 cal. I Oxidation Heat. Li20 . L40, . Na20 . N%02. K2O . K2O.i - Rb20 . cs20 . cs,o, . - 140 cal. I53 119 86-97-1 I34 I00 83'5-94'9 83-99 - 142 imaginary level v = 6023 can be attained. From the above it follows that the levels 6, (6900) and u3 (8248) can be excited by the simple oxidation process, whereas S4 (4412) and u4 (5077) are excluded. For those levels a deviation is to be expected, which the experiments have shown to exist. I n order to calculate the ratio of the intensities of the members of the subordinate series, we shall try to determine the transition probabilities, using for this purpose an hypothesis suggested by Bohr's correspondence principle. The classical theory gives for the intensity of the (T - I) har- monic of an anharmonic oscillator the formula where 0 is the frequency in the orbit and C, the coefficient in the Fourier development .If we consider an orbit with total quantum number n, and term frequency V, then o = - and the intensity for an emission characterised by a change T of the total quantum number is given by 2v n' The spectrum lines of the subordinate series correspond to transitions from different initial levels to the same final level. The intensities can be repre- sented by AC,Z(r . 2)' n where the quantum number n can take a series of values. A depends on the number of atoms in the initial states. I t is difficult to estimate the values of the constants C, but, the change of total quantum number being as large as possible in all transitions, it gives perhaps a good approximation as we make them all equal, I n this case the intensities are proportional to To get an idea of the value of the constant A, we may imagine that the heat of reaction acts in such a way, that atoms with a very high veIocity are formed.Then we can calculate A, by considering the equilibrium of the alkali-atoms in a gas of very high (imaginary) temperature. In this way w e find482 FLAME SPECTRA AND CHEMICAL REACTION where 8 is an imaginary temperature determined from the heat of reaction by k0 = specific heat of reaction. As the final result we obtain log 3 + 51og KO e = c + 4 log ( r , i) ( KO ) . * (1) Hence, if is plotted against T . 5 a straight line should result. To show the method of calculation, we give the following table for caesium (see p.483). log 3 + f_ log e FIG. 3.MISS C. E. BLEEKER 483 The quantum numbers have been determined from the term frequencies. Figures I to 4 give the graphical representation of equation I. The scale of the abscissz has been taken four times as large as that of the ordinates. The points are situated on a straight line, which forms an angle of 45 degrees with the axes. Equation I, therefore, actually represents our results very well for caesium and rubidium. For potassium the situation of the points 6, and u, is totally wrong. The question may be put as to whether those lines ought not to be interchanged. The experi- mental errors in the case of K are large, because the intensities and wave- length lie far from each other, but the mutual ratios of the lines (u4, a,), (u5* 8,) and so on are fairly accurate.The change of 6, and u4 would be in accordance with the notation given by Kayser,l who has interchanged both series. For the first members in the series of sodium we find large deviations, the values being much too large. We have shown that from the value of the heat of reaction a discontinuity is to be expected in the slope of the curve at the lines S3 and ur Now we find this discontinuity already at 6, and However, the experimental results of the lines a,, ~ ~ , . 8 ~ , a4, are much less reliable as those of the other lines, and the connection of the measurements of the lines below 6, and a, and those above 8, and u4 are till now given only by one experiment. An error of 10 per cent.can occur in the ratio 6, : 6, and then this error would also occur in a4, a,, u3, the connection being given by 6, : I hope in due course to publish in my dissertation further experimental results on this special case. In conclusion I venture to state that my investigations show that the older facts on the emission of flame spectra in the principal series and the new results on subordinate series can be explained on the basis of temperature radiation for the former and of chemical reaction for the latter. I f we do so, the agreement is very satisfactory. Kayser, Handbuch der Spectroxopie, Bd. 2, 523. FLAME SPECTRA AND CHEMICAL REACTION. BY MISS C. E. BLEEKER (UTRECHT).~ Communication received August 2 I st, I 9 z 5 . Measurements on the relative intensities of several members of the first and second subordinate series in the flame spectra of the elements rubidium and caesium have previously been published.2 The experiments have shown that the ratio of these intensities depends neither on the concentration of the salt in the flame, nor on its temperature.Also, for this kind of excitation the ratio of the doublets is found to be The change in the successive intensities of lines in a series due to tem- perature variation in the case of thermal excitation may be estimated in the following manner. If T represents the temperature, K the Boltzmann con- stant, e the energy and p the statistical weight of the level under considera- tion, then the number of atoms which are in the state 4,3 for the case of temperature equilibrium, may be represented by : 2 : I.while represents this number for the 5 state. number of possible transitions is given by : I f W , and W, represent the transition probabilities, then the ratio of the The ratio W, : W, is generally supposed to be independent of the tem- perature, and we find for the ratio of the transitions : where hC b = - k' It follows that the variation of this ratio, if we consider two temperatures TI and T,, is given by the formula : - b(v1 - V.) - - - e (TI, TI,) 1 Communicated by Professor L. S. Ornstein. 2 2. fiir Physik, 1924, Bd: 27, 195. 9 The notation of Fowler is used. 4 79480 FLAME SPECTRA AND CHEMICAL REACTION Now for the oxygen flame we may put T = 2700' and for an ordinary For the case of caesium, the variation of the ratio : bunsen T = I 700'.can be expected. The above-men tioned measurements have been extended to potassium and sodium, and far these alkalis also analogous results have been obtained. The measurements were much more complicated as the lines are situated in less favourable regions of the spectrum and therefore the results show much larger mutual deviation than was the case for the heavier alkalis. As the temperature has no influence on the ratio of the intensities, it is impossible for the subordinate series found in flames to be caused by ther- mal excitation alone. The experiment of Haber,l which shows the emis- sion of the D lines of sodium due only to chemical binding of Na with C1, suggests that in the case offlames also, chemical reaction plays a part.I n our case, it is possible that besides temperature-radiation, the oxidation of alkali atoms is the cause of the emission of spectral lines. Wecan imagine the process in the following way. All the x-levels can be formed by black body radiation from the a-level, which is the normal state of the unexcited atom. 'The simplest way of excitation of the other (T- and &levels, is by absorption through atoms in the first x state. The number of atoms in this state, however, is very small, afortiort' the number of atoms which have an electron in the higher U- and &orbits is still smaller. The ratio of the lines due to emission from those levels would, for the case under considera- tion, depend on the temperature but the lines will be very faint. Let us now consider the second cause.The Cs atoms can be oxidised to Cs,O, the specific heat of oxidation being 83-99 cal. (Landolt) or to Csa02, with oxidation-heat of 142 cal. In both cases the energy set free in the reaction can be used for the ionisation of an Cs-atom, the ionisation energy amounting to 88 cal. The latter process can be performed by radi- ation or by collisions of the second kind. The ionised atoms will emit radiation, and the distribution of the intensities of the different emission lines will be proportional to the apriuri probability of the respective levels and the transition probabilities. Therefore, the total intensity of each line is composed of two parts, one due to thermal excitation and the other to the oxidation process. For the lines of the subordinate series the oxidation process prevails, and this can give us an explanation of the fact that the temperature effect cannot be found.The lines of the principal series, however, are much stronger than those of the subordinate series. I n their emission the oxidation process plays only a subordinate part. Within the limits of experimental error they will possess the intensity given by Planck's law, as has been shown by measurements on the temperature of flames made with the resonance lines. In order to consider the same question in the case of the other alkalis, we give the following table (see p. 481). The table shows that in the case of the alkalis K and Na, the maximum value of the oxidation heat for the simple oxide is not high enough for total ionisation. For K the ionised state can still nearly be reached; in the case of Na,O, the oxidation heat is far less than the ionisation energy.For this alkali only the energy corresponding to the frequency @$ v,, is available, where v,, = 41449 represents the frequency of the normal state. The frequency under consideration amounts to 35426. Therefore the The experimental results do not show any variation. 1 Z. fur Physik, 1922, Bd. IX., 302.MISS C. E. BLEEKER Alkali Metal. L i . . . . N a . . . . K . . . . Rb. . . . c s . . . . Ionisation-Energy. 123 cal. I Oxidation Heat. Li20 . L40, . Na20 . N%02. K2O . K2O.i - Rb20 . cs20 . cs,o, . - 140 cal. I53 119 86-97-1 I34 I00 83'5-94'9 83-99 - 142 imaginary level v = 6023 can be attained. From the above it follows that the levels 6, (6900) and u3 (8248) can be excited by the simple oxidation process, whereas S4 (4412) and u4 (5077) are excluded.For those levels a deviation is to be expected, which the experiments have shown to exist. I n order to calculate the ratio of the intensities of the members of the subordinate series, we shall try to determine the transition probabilities, using for this purpose an hypothesis suggested by Bohr's correspondence principle. The classical theory gives for the intensity of the (T - I) har- monic of an anharmonic oscillator the formula where 0 is the frequency in the orbit and C, the coefficient in the Fourier development . If we consider an orbit with total quantum number n, and term frequency V, then o = - and the intensity for an emission characterised by a change T of the total quantum number is given by 2v n' The spectrum lines of the subordinate series correspond to transitions from different initial levels to the same final level.The intensities can be repre- sented by AC,Z(r . 2)' n where the quantum number n can take a series of values. A depends on the number of atoms in the initial states. I t is difficult to estimate the values of the constants C, but, the change of total quantum number being as large as possible in all transitions, it gives perhaps a good approximation as we make them all equal, I n this case the intensities are proportional to To get an idea of the value of the constant A, we may imagine that the heat of reaction acts in such a way, that atoms with a very high veIocity are formed.Then we can calculate A, by considering the equilibrium of the alkali-atoms in a gas of very high (imaginary) temperature. In this way w e find482 FLAME SPECTRA AND CHEMICAL REACTION where 8 is an imaginary temperature determined from the heat of reaction by k0 = specific heat of reaction. As the final result we obtain log 3 + 51og KO e = c + 4 log ( r , i) ( KO ) . * (1) Hence, if is plotted against T . 5 a straight line should result. To show the method of calculation, we give the following table for caesium (see p. 483). log 3 + f_ log e FIG. 3.MISS C. E. BLEEKER 483 The quantum numbers have been determined from the term frequencies. Figures I to 4 give the graphical representation of equation I. The scale of the abscissz has been taken four times as large as that of the ordinates.The points are situated on a straight line, which forms an angle of 45 degrees with the axes. Equation I, therefore, actually represents our results very well for caesium and rubidium. For potassium the situation of the points 6, and u, is totally wrong. The question may be put as to whether those lines ought not to be interchanged. The experi- mental errors in the case of K are large, because the intensities and wave- length lie far from each other, but the mutual ratios of the lines (u4, a,), (u5* 8,) and so on are fairly accurate. The change of 6, and u4 would be in accordance with the notation given by Kayser,l who has interchanged both series. For the first members in the series of sodium we find large deviations, the values being much too large. We have shown that from the value of the heat of reaction a discontinuity is to be expected in the slope of the curve at the lines S3 and ur Now we find this discontinuity already at 6, and However, the experimental results of the lines a,, ~ ~ , . 8 ~ , a4, are much less reliable as those of the other lines, and the connection of the measurements of the lines below 6, and a, and those above 8, and u4 are till now given only by one experiment. An error of 10 per cent. can occur in the ratio 6, : 6, and then this error would also occur in a4, a,, u3, the connection being given by 6, : I hope in due course to publish in my dissertation further experimental results on this special case. In conclusion I venture to state that my investigations show that the older facts on the emission of flame spectra in the principal series and the new results on subordinate series can be explained on the basis of temperature radiation for the former and of chemical reaction for the latter. I f we do so, the agreement is very satisfactory. Kayser, Handbuch der Spectroxopie, Bd. 2, 523.

ISSN:0014-7672    

DOI:10.1039/TF9262100479

出版商:RSC    

年代:1926

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. CONCERNING THE FUNDAMENTAL LAWS OF PHOTO- CHEMISTRY. BY PROFESSOR IVAN PLOTNIKOW (ZAGREE). Communication received Jz@ I 3 th, I 9 2 5 . The development of every scientific study may be divided into three phases,-the first, the chaotic, in which an accumulation of experimental data takes place, and confusion of opinion prevails ; the second, that of the establishment of its fundamental laws, and the classification and systematisa- tion of the experimental material; and the third, which is the normal progress of the science as such, accompanied by its vigorous development in its applied form. Photochemistry is at present in the second stage which, as a matter of fact, always represents a turning-point in the history of a given branch of science.For this reason, too, our meeting of to-day must, perforce, be considered one of an historic nature, and if it fails to clear up the burning questions in our science, a continuation in the near future of to-day’s dis- cussion would appear necessary. This second stage is always relatively brief, and is characterised by great intellectual exertion on the part of the leading investigators, as well as by the sharp clash of mutually opposing tendencies. After these introductory words, we may proceed to the discussion of the main question of the day, to wit, which are the experiences in photo- chemistry which we must accept as fundamental laws. I t is now more than a hundred years ago since Theodore Grotthus proclaimed (in 1817), that only the light absorbed by a solid body is capable of photochemical action.From his day to ours there has been no case on record to which this rule does not apply, i.6. where it was not the absorbed light that was the determining factor, but some other light, such as reflected or filtered light. And we may be sure that the future, too, will hold no instance of a chemical reaction of light in which this law will not hold good; because this phenomenon lies in the very nature of photochemical reactions as stationary 1 processes which occur at the expense of energy supplied from without. Wherefore it follows that only the energy arrested by the said solid body can exercise any influence upon it. A phenomenon or rule of such general application must needs be classified as a fundamental law, the meaning and importance of which is even to-day not yet clear to many investigators ; by Grotthus’ contemporaries it was not understood at all and soon totally forgotten.Draper (in 1840), and many others had to re- discover it, and only in recent years has it received due attention. Hence it is not astonishing that investigators should have sought to apply the 484PROFESSOR IVAN PLOTNIKOW 4% already familiar principles of ordinary reactions-such as the law of mass action-to photochemical reactions as well. The first to do this was Wittwer (in 1854)2 who, from the result of a single investigation, drew the conclusion that photochemical reactions, too, follow the law of mass action as laid down by Guldberg and Waage; with this difference, that the velocity of reaction constant was still to be multiplied by the intensity of the light producing the effect.Later on, Nernst completely endorsed this view, and it took a long time before its correctness began to be doubted. Had investigators grasped the underlying sense of Grotthus’ law sooner, they would have been forced to the conclusion that it is not the intensity and the chemical mass which must be thedetermining and regulating factors in the process of photochemical reaction, but solely the absorbed light energy ; and that there must also b? a quantitative relation between the quantity of matter transformed and the absorbed light energy. The only question is, by what functi )n this relation is to be rendered.If we indicate the velocity of photochemical reaction (i.e. the quantity of matter transformed per time unit) by V, and the absorbed light energy (to be determined in accordance with Beer’s law) by A, we get the general formula- v = f(A). This formula is the necessary deduction from the Grotthus law ; it is, however, as we have seen, in general terms and says nothing about the form of the function. Van’t Hoff expressed the view (in 1904) that a simple linear ratio of proportion nust obtain here, i.e. that the quantitative expression of Grotthus’ law must assume the following form :- v = KA, in which case K represents the chemically individual constant of velocity of reaction. Direct proof, no less than a series of deductions entailed by this formula, have confirmed its correctness, and we are now justified in ac- cepting it as a quantitative extension of the first law, and in combining it with the latter under the joint name of the Grotthus-van’t Hoff law of photochemical absorption.Realising to the full the far-reaching significance of this law, so far back as in 19x0 I pronounced it one of the fundamental bases of photo- chemistry, and have striven ever since to define it further, to apply it mathematically to all possible special cases and, so far as possible, to make experimental proof of my deductions. This field of research has proved exceedingly large and thorny, but also fruitful and rich in possibilities, Among the most interesting consequences of the photochemical law of absorption are the spatially progressive light reactions, the necessary ex- istence of which I had at the time deduced from this law, and whose actual existence has also been demonstrated and their progress measured.I t would be interesting to study this type of reaction more closely, because the method of investigation is very simple in these cases and the photo- chemical properties come out very strongly in them. But modern photochemical literature shows very considerable and curious divergencies from this straight line of investigation, as practically dictated by this law; and not only divergency is observable, but even retrogression. To take an instance, in 1922 Wegscheider fell back again on the old Nernst-Wittwer formula, and has since then been trying to compute afresh the special cases the mathematics of which had been first 32486 THE FUNDAMEN’I’AL LAWS OF PHO’I’OCHEMISTR\’ worked out by me.His fundamental idea is that in the thin layers the velocity of photochemical reaction is proportionate, not to the absorbed amount of light, but to the intensity of light prevailing at that particular spot. This hypothesis I hold to be in contradiction with the sense of Grotthus’ law as well as with experience ; wherefore, I cannot attach any photochemical value to this formulz, the final expression of which, by the way, in most cases coincides with mine; for even in the most tenuous of layers the reaction must proceed proportionately to the energy absorbed in this layer. This is in accordance with the Grotthus-van’t HOTS law, and experience bears it out.I need only refer to a little-known class-room ex- periment of Lasareff’s * which consists in throwing light from two sources at unequal distances on to two very thin collodion films of cyanine of equd composition (the result will be still better if thiosinamine is added by way of catalyser). A rotating sector is placed in the path of the rays from the nearer source of light, reducing the light to such an extent that the amount of light falling on the two films is the same in each case, although the intensity differs. If the Wttwer-Nernst-Wegscheider hypo- thesis were correct, the film exposed to the greater intensity would bleach more rapidly. But the experiment yields equal speed in the matter of bleaching, which is as it should be according to the Grotthus-van’t Hoff law.While these events were in progress in photochemistry, physics had experienced far-reaching revolutions, which could not fail to influence photo- chemistry, which is a border province between physics and chemistry. During those years, Stoietow, Lenard, and Hallwachs discovered and in- vestigated photochemical phenomena, special credit being due to Lenard. I t was proved that the mobility of electrons expelled by light is independent of the intensity of the light and proportionate to the frequency. About the same time Planck demonstrated that the absorption and emission of light, which are by nature photo-electrical phenomena, take place by quanta ; which is to say that the magnitude of energy hv (in which Ir, represents Planck’s constant of radiation and v the frequency) is a determining factor in this process.Einstein connected these two facts, and expressed the opinion that the motivity of the electron detached by the photo-electric effect of the energy of light must be equal to Av, i.e. I t is obvious that this law is merely a deduction from the first main principle and is strictly applicable only to free electrons. In all other cases it becomes all the more inapplicable, the more firmly the electrons are bour,d. In the case of metals and sundry other bodies possessing electrons which are very easily detachable, practical applicability of this law was to be expected, as is, indeed, proved by fact. But in the case of selective ab- sorption and other cases, when great chemical forces have to be overcome in order to bring about the detachment of the electrons from the molecular group, it cannot apply any longer, which circumstance is, moreover, cor- roborated by fact. This notwithstanding, Einstein postulated yet another hypothesis, viz.that photochemical processes were likewise subject to this purely photo-physical law, which is obviously nonsense, because it means the forcible elimination of the chemical principle from photochemistry. As this moment (of Einstein’s announcement) happened to coincide with many great events of world importance, which rather unbalanced the established order of things in many cases and naturally did not fail to influence evenPROFESSOR IVAN PLOTNIKOW 487 science, this hypothesis was without any adequate grounds raised to the dignity of a fundamental law of photochemistry, despite the fact that it yielded deviations from the experiment to the extent of decillions per cent.Over one hundred per cent. was practically the average. I first pointed out the untenableness of this so-called law in the years 1920-~2.~ I assume that most of you are acquainted with my proofs and objections, and therefore refrain from a repetition of them, which would in any case take up too much time. Had Einstein’s idea, however, been accepted merely as a working hypothesis in the sense that if the absorption happens to be a process by quanta, then the photochemical effect must likewise be a function of h~ ; and if this function had been sought experimentally and theoretically, much would have been gained thereby.Latterly there have been increasing signs of improvement, and the matter is beginning to be judged more critically. Most distinctly is this to be seen in the utterances of Nernst, at one time one of the most zealous champions of this law. In 1920 he was still a staunch believer in i t ; in T 92 2 one could perceive his first doubts of it at the Naturforscherversammlung in Leipzig ; in 1923 he speaks of the incompleteness of this law, expressing himself almost literally in the same terms as I had done in my book ‘‘ Out- lines of Photochemistry ’) (Grundrisse der Phtochemie, 1923) and in 1925 he dismisses this so-called law briefly in the following words : “ I n the assumption that this must always be so, much was said about a law of photochemical equivalence, for which there is, however, no occasion in theory, tzor can any foundation based on experiment be adduced for if.” I think the time has come for us to consider this question as disposed of; to re-establish the working hypothesis that the photochemical effect is a function of hv; and to determine the form of this function.If we state the problem in this way, the quantum theory as applied to light reactions does not come into conflict with the Grotthus-van’t Hoff law; but the latter is rendered more profound in the light of the quantum theory. For this purpose it suffices in the general equation-- v = kA to represent the constant of velocity of reaction k as a function of Av. All formulae so far deduced on the basis of this law remain; the chemical principle in photochemical reactions is preserved; and the formulae are merely enlarged so as to indicate the functional dependence of photo- chemical reaction upon wave-lengths as well.Over the determination of formulz for all possible special cases many problems arise which will yet have to be extensively discussed; but of this I will speak in my second paper. The above shows that at this moment we have to deal with three tendencies, causing considerable confusion, especially for beginners. And hence it is necessary to clear up matters completely and to determine finally what is to be accepted as a fundamental law of photochemistry; what as a working hypothesis; and what ought to be rejected altogether. For this purpose I venture to draw up the following three theses for discussion by this meeting, in the hope that thereby the matter will indeed be cleared up :- Thsis I.The intensity conception of Wittwer-Nernst-Wegscheider ought to be dropped as quite mistaken. Thesis II; The Grotthus-van’t Hoff law of photochemical absorption must be accepted as a fundamental law, based on experience, and moreover inherent in the nature of photochemical processes as stationary processes.488 THE FUNDAMENTAL LAWS O F PHOTOCHEMISTRY Thesis III. Einstein’s so-called law of photochemical equivalence, in its hitherto accepted form, must be dropped as altogether mistaken. On the other hand, the experience based on the quantum theory must be utilised as a basis for extension and elaboration of the Grotthus-van’t Hoff fundamental law.REFERENCES. 1 Plotnikow, Lehrb. d . allgem. Photochemic, p. 67, Berlin (1920). 9 Plotnikow, Lchrb. d. allgem Photochemic, p. 133, Berlin (1920). 3 Wegscheider, Zeit. f . physik. Chem. 103, p. 273 (1922). Cf. my notes upon the work, Rec. trav. chim depajs-bas, 4. p. 798 (1925). 4 Plotnikow, Grundriss der Photochcmte, p. 10. Berlin (1923). 5 Plotnikow, Allgem. Photochem. (1920). Gvundriss der Photochemie (1923). Zeit. f. Wiss. Photogr. 21, s. 137 (1922); 22, s. 108 (1923). 6 Nernst und Noddak, B e d Akud., p. 110 (1923). 7 Nernst, Wienei ncue frke Presse, No. 21766, Sunday, 19 April, s. 7 (192j). Zagreb, gfh Jzd., I g 2 5, Phys. Chm. Insfifuf. KgZ. T e c h . Nochchule. CONCERNING THE FUNDAMENTAL LAWS OF PHOTO- CHEMISTRY. BY PROFESSOR IVAN PLOTNIKOW (ZAGREE).Communication received Jz@ I 3 th, I 9 2 5 . The development of every scientific study may be divided into three phases,-the first, the chaotic, in which an accumulation of experimental data takes place, and confusion of opinion prevails ; the second, that of the establishment of its fundamental laws, and the classification and systematisa- tion of the experimental material; and the third, which is the normal progress of the science as such, accompanied by its vigorous development in its applied form. Photochemistry is at present in the second stage which, as a matter of fact, always represents a turning-point in the history of a given branch of science. For this reason, too, our meeting of to-day must, perforce, be considered one of an historic nature, and if it fails to clear up the burning questions in our science, a continuation in the near future of to-day’s dis- cussion would appear necessary.This second stage is always relatively brief, and is characterised by great intellectual exertion on the part of the leading investigators, as well as by the sharp clash of mutually opposing tendencies. After these introductory words, we may proceed to the discussion of the main question of the day, to wit, which are the experiences in photo- chemistry which we must accept as fundamental laws. I t is now more than a hundred years ago since Theodore Grotthus proclaimed (in 1817), that only the light absorbed by a solid body is capable of photochemical action. From his day to ours there has been no case on record to which this rule does not apply, i.6.where it was not the absorbed light that was the determining factor, but some other light, such as reflected or filtered light. And we may be sure that the future, too, will hold no instance of a chemical reaction of light in which this law will not hold good; because this phenomenon lies in the very nature of photochemical reactions as stationary 1 processes which occur at the expense of energy supplied from without. Wherefore it follows that only the energy arrested by the said solid body can exercise any influence upon it. A phenomenon or rule of such general application must needs be classified as a fundamental law, the meaning and importance of which is even to-day not yet clear to many investigators ; by Grotthus’ contemporaries it was not understood at all and soon totally forgotten.Draper (in 1840), and many others had to re- discover it, and only in recent years has it received due attention. Hence it is not astonishing that investigators should have sought to apply the 484PROFESSOR IVAN PLOTNIKOW 4% already familiar principles of ordinary reactions-such as the law of mass action-to photochemical reactions as well. The first to do this was Wittwer (in 1854)2 who, from the result of a single investigation, drew the conclusion that photochemical reactions, too, follow the law of mass action as laid down by Guldberg and Waage; with this difference, that the velocity of reaction constant was still to be multiplied by the intensity of the light producing the effect. Later on, Nernst completely endorsed this view, and it took a long time before its correctness began to be doubted. Had investigators grasped the underlying sense of Grotthus’ law sooner, they would have been forced to the conclusion that it is not the intensity and the chemical mass which must be thedetermining and regulating factors in the process of photochemical reaction, but solely the absorbed light energy ; and that there must also b? a quantitative relation between the quantity of matter transformed and the absorbed light energy.The only question is, by what functi )n this relation is to be rendered. If we indicate the velocity of photochemical reaction (i.e. the quantity of matter transformed per time unit) by V, and the absorbed light energy (to be determined in accordance with Beer’s law) by A, we get the general formula- v = f(A).This formula is the necessary deduction from the Grotthus law ; it is, however, as we have seen, in general terms and says nothing about the form of the function. Van’t Hoff expressed the view (in 1904) that a simple linear ratio of proportion nust obtain here, i.e. that the quantitative expression of Grotthus’ law must assume the following form :- v = KA, in which case K represents the chemically individual constant of velocity of reaction. Direct proof, no less than a series of deductions entailed by this formula, have confirmed its correctness, and we are now justified in ac- cepting it as a quantitative extension of the first law, and in combining it with the latter under the joint name of the Grotthus-van’t Hoff law of photochemical absorption.Realising to the full the far-reaching significance of this law, so far back as in 19x0 I pronounced it one of the fundamental bases of photo- chemistry, and have striven ever since to define it further, to apply it mathematically to all possible special cases and, so far as possible, to make experimental proof of my deductions. This field of research has proved exceedingly large and thorny, but also fruitful and rich in possibilities, Among the most interesting consequences of the photochemical law of absorption are the spatially progressive light reactions, the necessary ex- istence of which I had at the time deduced from this law, and whose actual existence has also been demonstrated and their progress measured.I t would be interesting to study this type of reaction more closely, because the method of investigation is very simple in these cases and the photo- chemical properties come out very strongly in them. But modern photochemical literature shows very considerable and curious divergencies from this straight line of investigation, as practically dictated by this law; and not only divergency is observable, but even retrogression. To take an instance, in 1922 Wegscheider fell back again on the old Nernst-Wittwer formula, and has since then been trying to compute afresh the special cases the mathematics of which had been first 32486 THE FUNDAMEN’I’AL LAWS OF PHO’I’OCHEMISTR\’ worked out by me. His fundamental idea is that in the thin layers the velocity of photochemical reaction is proportionate, not to the absorbed amount of light, but to the intensity of light prevailing at that particular spot.This hypothesis I hold to be in contradiction with the sense of Grotthus’ law as well as with experience ; wherefore, I cannot attach any photochemical value to this formulz, the final expression of which, by the way, in most cases coincides with mine; for even in the most tenuous of layers the reaction must proceed proportionately to the energy absorbed in this layer. This is in accordance with the Grotthus-van’t HOTS law, and experience bears it out. I need only refer to a little-known class-room ex- periment of Lasareff’s * which consists in throwing light from two sources at unequal distances on to two very thin collodion films of cyanine of equd composition (the result will be still better if thiosinamine is added by way of catalyser).A rotating sector is placed in the path of the rays from the nearer source of light, reducing the light to such an extent that the amount of light falling on the two films is the same in each case, although the intensity differs. If the Wttwer-Nernst-Wegscheider hypo- thesis were correct, the film exposed to the greater intensity would bleach more rapidly. But the experiment yields equal speed in the matter of bleaching, which is as it should be according to the Grotthus-van’t Hoff law. While these events were in progress in photochemistry, physics had experienced far-reaching revolutions, which could not fail to influence photo- chemistry, which is a border province between physics and chemistry.During those years, Stoietow, Lenard, and Hallwachs discovered and in- vestigated photochemical phenomena, special credit being due to Lenard. I t was proved that the mobility of electrons expelled by light is independent of the intensity of the light and proportionate to the frequency. About the same time Planck demonstrated that the absorption and emission of light, which are by nature photo-electrical phenomena, take place by quanta ; which is to say that the magnitude of energy hv (in which Ir, represents Planck’s constant of radiation and v the frequency) is a determining factor in this process. Einstein connected these two facts, and expressed the opinion that the motivity of the electron detached by the photo-electric effect of the energy of light must be equal to Av, i.e.I t is obvious that this law is merely a deduction from the first main principle and is strictly applicable only to free electrons. In all other cases it becomes all the more inapplicable, the more firmly the electrons are bour,d. In the case of metals and sundry other bodies possessing electrons which are very easily detachable, practical applicability of this law was to be expected, as is, indeed, proved by fact. But in the case of selective ab- sorption and other cases, when great chemical forces have to be overcome in order to bring about the detachment of the electrons from the molecular group, it cannot apply any longer, which circumstance is, moreover, cor- roborated by fact.This notwithstanding, Einstein postulated yet another hypothesis, viz. that photochemical processes were likewise subject to this purely photo-physical law, which is obviously nonsense, because it means the forcible elimination of the chemical principle from photochemistry. As this moment (of Einstein’s announcement) happened to coincide with many great events of world importance, which rather unbalanced the established order of things in many cases and naturally did not fail to influence evenPROFESSOR IVAN PLOTNIKOW 487 science, this hypothesis was without any adequate grounds raised to the dignity of a fundamental law of photochemistry, despite the fact that it yielded deviations from the experiment to the extent of decillions per cent. Over one hundred per cent.was practically the average. I first pointed out the untenableness of this so-called law in the years 1920-~2.~ I assume that most of you are acquainted with my proofs and objections, and therefore refrain from a repetition of them, which would in any case take up too much time. Had Einstein’s idea, however, been accepted merely as a working hypothesis in the sense that if the absorption happens to be a process by quanta, then the photochemical effect must likewise be a function of h~ ; and if this function had been sought experimentally and theoretically, much would have been gained thereby. Latterly there have been increasing signs of improvement, and the matter is beginning to be judged more critically. Most distinctly is this to be seen in the utterances of Nernst, at one time one of the most zealous champions of this law.In 1920 he was still a staunch believer in i t ; in T 92 2 one could perceive his first doubts of it at the Naturforscherversammlung in Leipzig ; in 1923 he speaks of the incompleteness of this law, expressing himself almost literally in the same terms as I had done in my book ‘‘ Out- lines of Photochemistry ’) (Grundrisse der Phtochemie, 1923) and in 1925 he dismisses this so-called law briefly in the following words : “ I n the assumption that this must always be so, much was said about a law of photochemical equivalence, for which there is, however, no occasion in theory, tzor can any foundation based on experiment be adduced for if.” I think the time has come for us to consider this question as disposed of; to re-establish the working hypothesis that the photochemical effect is a function of hv; and to determine the form of this function.If we state the problem in this way, the quantum theory as applied to light reactions does not come into conflict with the Grotthus-van’t Hoff law; but the latter is rendered more profound in the light of the quantum theory. For this purpose it suffices in the general equation-- v = kA to represent the constant of velocity of reaction k as a function of Av. All formulae so far deduced on the basis of this law remain; the chemical principle in photochemical reactions is preserved; and the formulae are merely enlarged so as to indicate the functional dependence of photo- chemical reaction upon wave-lengths as well.Over the determination of formulz for all possible special cases many problems arise which will yet have to be extensively discussed; but of this I will speak in my second paper. The above shows that at this moment we have to deal with three tendencies, causing considerable confusion, especially for beginners. And hence it is necessary to clear up matters completely and to determine finally what is to be accepted as a fundamental law of photochemistry; what as a working hypothesis; and what ought to be rejected altogether. For this purpose I venture to draw up the following three theses for discussion by this meeting, in the hope that thereby the matter will indeed be cleared up :- Thsis I. The intensity conception of Wittwer-Nernst-Wegscheider ought to be dropped as quite mistaken. Thesis II; The Grotthus-van’t Hoff law of photochemical absorption must be accepted as a fundamental law, based on experience, and moreover inherent in the nature of photochemical processes as stationary processes.488 THE FUNDAMENTAL LAWS O F PHOTOCHEMISTRY Thesis III. Einstein’s so-called law of photochemical equivalence, in its hitherto accepted form, must be dropped as altogether mistaken. On the other hand, the experience based on the quantum theory must be utilised as a basis for extension and elaboration of the Grotthus-van’t Hoff fundamental law. REFERENCES. 1 Plotnikow, Lehrb. d . allgem. Photochemic, p. 67, Berlin (1920). 9 Plotnikow, Lchrb. d. allgem Photochemic, p. 133, Berlin (1920). 3 Wegscheider, Zeit. f . physik. Chem. 103, p. 273 (1922). Cf. my notes upon the work, Rec. trav. chim depajs-bas, 4. p. 798 (1925). 4 Plotnikow, Grundriss der Photochcmte, p. 10. Berlin (1923). 5 Plotnikow, Allgem. Photochem. (1920). Gvundriss der Photochemie (1923). Zeit. f. Wiss. Photogr. 21, s. 137 (1922); 22, s. 108 (1923). 6 Nernst und Noddak, B e d Akud., p. 110 (1923). 7 Nernst, Wienei ncue frke Presse, No. 21766, Sunday, 19 April, s. 7 (192j). Zagreb, gfh Jzd., I g 2 5, Phys. Chm. Insfifuf. KgZ. T e c h . Nochchule.

ISSN:0014-7672    

DOI:10.1039/TF9262100484

出版商:RSC    

年代:1926

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. EINSTEIN’S LAW OF PHOTOCHEMICAL EQUIVALENCE. BY PROFESSOR N. R. DHAR AND B. K. MUKERJI (ALLAHABAD). Commzcnication received August 2 qth, I 9 2 5. Though Einstein gave out his law before the advent of the Bohr theory of atomic structure, recent researches show that the law of photochemical equivalence can follow as a natural sequence of the Bohr theory of atoms and molecules. According to the quantum concepts of energy the first effect of absorption of energy by a molecule or an atom is to lift up an electron to a higher orbit, so that the atom or molecule receiving light energy gains in internal energy. I n the following tables, a summary is given of the reactions hitherto tried to test the applicability of Einstein’s law.TABLE I. ~~ Reaction. 3 0 , = 2 0 3 . . . . . 20, +. C1, = 3 0 , I- C1, . . . Bromine and cyclohexane . . Chlorine and tri-chloromethane . Ozonisation ofoxygen . . . Photolysis of ketones, aldehydes and aliphatic acids . . . Decomposition of C10, . . . Decomposition of C1,O . . . 2CC1,Br + C1, = 2CC4 + Br, . 2CC1,Br + 0, = 2COC1, i- Br, + C1, Author. Bodenstein (2. physik. Bodensttin (foc. cit.) Noddack (2. Elektrochem., Noddack (roc. cit.) Warburg (2. Elektrochem, Volmer (Compt. rend., Bowen (your. Chem. SOC., Bowen (your. Chent. SOL, Griiss ( Z . Elektrochem, Griiss (lor. cit.) Chem., 1913, 85, 229) I921,2 9 859) I920,6 54) 19249 178,697) 1923, 123, 1199) 1923,1239 2328) 1923,299 144) Molecules per Quanta.1 0.96 (2070 tf) I I (Preliminary experiment) I I From Tables I. and 11. it will be seen that the law is applicable only to a few cases, but it breaks down in a large number of cases. I t is now generally held that the light energy is responsible only for the primary change in a photochemical reaction. The subsequent course of the reaction depends on several factors such as the heat energy evolved during the primary process, the radiations received from the light source and the phase conditions of the molecules involved. The thermodynamic proof of Einstein’s law rests on the conception of an ideal perfectly reversible photochemical reaction. Of course, to realise 489490 EINSTEIN'S LAW OF PHOTOCHEMICAL EQUIVALENCE Reaction. Anthracene 3 Dianthracene .. C,H,NO COOH H 2 + C12=2HCl. . . 203+3C2 . . . . . CH,COCH, + H,O = CH, -t CH,. COOH Decomposition of hydrogen peroxide Oxidation of quinine . . . Br + C,H, = HBr + C H Br . Photolysis of hydrogen io6de . Photolysis of hydrogen bromide . Ozone decomposition in He . . Decomposition of ammonia . . Decomposition of aqueous KN 0: . Fumaric +, maleic acid . . Maleic -> fumaric acid . . Decomposition of silver bromide emulsions on photographic plates . . . . . Potassium oxalate and iodine , Ferrous sulphate and iodine . . Sodium nitrite and iodine . . Potassium formate and iodine . Calcium lactate and bromine . 0 - CSH NOZCHO + co I- c1, = COCl, . . . Auto-oxidation of benzaldehyde . N%S03 + 0 = N% - SO, . . Bromine and tartaric acid . . Bromine and cinnamic acid .. Transformation of allocinnamyli- dene acetic acid +. normal form . . . . . Photo-decomposition of potassium permanganate . . . Decomposition of NC1, . . . Decomposition of nitrosyl chloride Decomposition of solution of oxalic acid in presence of uranyl nitrate . . . . . Bromine and stilbene . . . TABLE 11. -______ Author. Bodenstein (Z. physik. Chem., 1913, 85, 229) ,7 9 9 9 , 1 , 9 , ,, 9' 9 , Y ? 7 3 ,¶ 1 9 9 9 9 , 9 Wariurg (Z.'klektri:hem, 1920, 26, 54) 3 , 3 , Y, 7, 1 , I , ,> $ 9 9' Y , 9 9 9 9 1 9 *, Y Y 9 , 7 , , 9 Eggert and Noddack (Sitzs. Preuss. Akad. Wiss., Berlin, 1921, 631) Mukerji and Dhar 9 , Y Y 9 , 9 9 9 ) 9 , 7 9 9 , Gh&h and Basu (Private communication) Backstrom (Taylor's Phjs. Chem., p. 1241) Ghosh and Mukherji (Private communication) Ghosh and Purkayastha Ghosh and Gupta (Private Rideal and Norrish (Proc.Bowen (Joiir. Chenr. Soc., Bowen and Sharp (Jour. Chcm. Soc., 1925, 17, 1026) Boll (Compf. rend., 1913, 3hosh and Purkayastha communication) ROJI. SOC., 1923, 103, 342) 1923, 123,1199) 156, 1891) . _ ~ _ _ _ _ _. Molecules per Quanta. 0-25 1-0'33 'I1 100- 1000 106 200 I00 1-200 I 0 0 106 2 > - 0.85 (A = 2530 A) 0.23 0.25 0.03 0'1 I 3-01 (A = 4078 A) 0'032 0'063 0.026 I0 Many molecules re- act for each energy quanta Many molecules re- act for each energy quanta absorbed 9, 4-12 436 0'5 0.27- I * 18 1.5 (4480 A-5000 A) Less than I 305 practically the ideal condition is an impossibility and hence it is not for us to expect the photoequivalence law to hold in every case. I t is to be observed that most of the reactions in which Einstein's lau- breaks down are exothermic in nature as already remarked in a previous paper. The large amount of energy liberated in these exothermic reactions undoubtedly makes them too complicated for the simple law of photo-PROFESSOR N.R. DHAR AND B. K. MUKERJI 491 chemical equivalence to hold. It seems reasonable that Einstein’s law of photo-equivalence would be more readily applicable to endothermic reactions than to exothermic ones, because in endothermic reactions the light energy absorbed will be utilised wholly or mainly in bringing about the chemical transformation. This statement seems to be borne out by the fact that the reactions in which Einstein’s law holds (Table I.) are mostly endothermic in nature.l Again, Einstein’s expression Q = ~ z h is valid only for one particular wave-length.But, not only light of a definite wave-length can bring about activation but also a band which consists of light .Bf several wave-lengths is usually employed as the light source. From the Bohr point of view it seems likely that only one frequency at a time can bring about activation in a particular case. I t follows therefore, that when the strictest regard is not paid in selecting only the appropriate wave-length the attempt to apply Einstein’s law to a photochemical reaction is not expected to be a success. The filndamental simplicity of Einstein’s law can be fully realised if we restrict our attention only to the primary change in a reaction; but as a matter of fact there is reason to believe that a whole series of frequencies can activate a reaction and this tends to prove the formation of intermediate stages in a reaction, each of which only after the absorption of its char- acteristic frequency would pass to the next stage in the reaction.In order to explain the abnormally large photochemical yield in such exothermal reactions as the combination of hydrogen and chlorine, decompositions of hydrogen peroxide, ozone, etc., we suggest the following explanation based on the emission of ions and electrons in chemical changes :- I t is well known that ions are generated in the combination of oxygen and phosphorus, Similarly Richardson 2 has shown that when metals like Nay K, or alloys of these metals combined with Cl,, COCl, etc., ions are given out.Basing on these facts, we suggest the following mechanism of the combination of chlorine and hydrogen in presence of light. When a mixture of chlorine and hydrogen is illuminated, the chlorine molecule is converted into the active condition by the absorption of light. The activated chlorine molecules can now react with hydrogen molecules. This exothermic chemical change gives out radiation and high moving electrons. These electrons would in their turn activate further molecules of chlorine and these activated chlorine molecules would furthur combine with molecules of hydrogen and this process would continue ; Cl, + hvo = C1, (active) Electron + C1, = C1, (active). C1, (active) + H, = zHC1 + electron + heat energy A similar line of argument can be advanced in explaining the abnormalIy large yield in the photodecomposition of hydrogen peroxide, ozone etc.As has previously been observed in a foregoing paper we can explain the cases of poor photochemical yield as follows : since it has been postu- lated that photochemical changes take place by the formation of activated molecules by the radiant light energy it may be observed that all the collisions of the activated constituent with the rest of the inactive molecules may not be effective in bringing about the chemical change, and by ineffec- tive collision the activated molecule loses its extra amount of energy ’Compare Baly and Barker, your*. Cliem. SOC., 1921, 11% 653. 2 Plzil. Trans., 1921, 222, A, I.492 EINSTEIN’S LAM’ OF PHOTOCHEMICAL EQUIVALENCE and reverts to the inactive state.Hence, the total energy supplied to the system does not wholly contribute to the chemical transformation ; some of the energy being dissipitated to the surroundings. I t is interesting indeed, that a low degree of energy utilisation is characteristic not only of photo- chemical reactions but of chemical changes induced by a-rays and X-rays. Warburg explains poor photochemical yield on the assumption of a primary splitting into atoms which would require much more energy t.han would be represented by the net result of the reaction after their recombina- tion to form new molecules. But it is- extremely doubtful whether a primary splitting up of atoms is at all necessary for a photochemical reaction to proceed. I t must be emphasised at this stage that in all cases the energy level of the activation of atoms and molecules need not exactly correspond with the resonance or ionisation potential of the molecule or the atom concerned.In this connection a recent work by Rideal and Williams’ on the inter- action of ferrous ion and iodine would be of interest. The above authors conclude from their experiment: that the reaction is unimolecular with respect to iodine and h = 5790 A is effective in this change and this wave- length corresponds to 2.14 volts. They have further remarked that this value is practically equal to the resonance potential of iodine molecule (2.34 & - 2 volts) as given in Foote and Mohler’s “Origin of Spectra” page 67. These conclusions of the above authors are doubtful as will be shown from the following facts :- I n a foregoing paper we have shown that the reaction between ferrous sulphate and iodine in light is semi-molecular with respect to iodine. 111 other words, iodine in the atomic condition is reactive in this change. Moreover, from our present knowledge on ionisation and resonance potentials we conclude that these values are really concerned with the elements in the atomic conditions and not in the molecular state.We are of the opinion that the energy in the activated condition should be slightly less than the corresponding resonance potential of the active element in question and this is corroborated by the experimental results obtained in the reaction between iodine and ferrous sulphate in which it will be noted that the resonance potential of iodine atoms and not molecules as assumed by Rideal and Williams has the value 2-34 volts and the activation potential has the value 2.14.I t seems remarkable, however, that investigators in this line with all shades of opinion hardly ever question the soundness of Einstein’s law. The law states that each single molecule of a photo-sensitive substance requires just one quantum h,, of the requisite frequency v0 in order that it may be decomposed. On the Hohr theory, however, the absorption of a single quantum of every htv, signifies simply the interorbital transition of an electron inside the atom. Thus, of course, one can easily conceive that by the absorption of a quantum of‘ energy of the requisite magnitude an atom may be decomposed.As a logical consequence of this Einstein’s law is easily comprehensible in cases of monatomic molecules but when, say, diatomic molecules are involved this law obviously loses much of its significance. The present stage of our physical knowledge about molecules does not warrant us to attribute the decomposition of molecules as well to the simple interorbital transition of an electron. lyour. CIICIJZ. SOL., 192j, 127, 25s.PROFESSOR N. R. DHAR AND B. K. MUKERJI 493 Summary. (i) From a survey of the experimental results hitherto obtained, it is found that Einstein’s law of photoequivalence breaks down in the majority of cases. (ii) In our opinion Einstein’s law should be more applicable to endothermic reactions -than to exothermic ones. (iii) The abnormally large yield obtained in the photochemical combina- tion of hydrogen and chlorine has been explained from the point of view of electron emission during the interaction of activated chlorine molecules with hydrogen to form hydrochloric acid.The electrons thus emitted further activate more chlorine molecules and as such supplements tbe effect of light as a source of activation. Chemicn Z Laboratory, Alluhbad Uainersity, Adzahbad (India), August 3 ~ d , 1925. EINSTEIN’S LAW OF PHOTOCHEMICAL EQUIVALENCE. BY PROFESSOR N. R. DHAR AND B. K. MUKERJI (ALLAHABAD). Commzcnication received August 2 qth, I 9 2 5. Though Einstein gave out his law before the advent of the Bohr theory of atomic structure, recent researches show that the law of photochemical equivalence can follow as a natural sequence of the Bohr theory of atoms and molecules.According to the quantum concepts of energy the first effect of absorption of energy by a molecule or an atom is to lift up an electron to a higher orbit, so that the atom or molecule receiving light energy gains in internal energy. I n the following tables, a summary is given of the reactions hitherto tried to test the applicability of Einstein’s law. TABLE I. ~~ Reaction. 3 0 , = 2 0 3 . . . . . 20, +. C1, = 3 0 , I- C1, . . . Bromine and cyclohexane . . Chlorine and tri-chloromethane . Ozonisation ofoxygen . . . Photolysis of ketones, aldehydes and aliphatic acids . . . Decomposition of C10, . . . Decomposition of C1,O . . . 2CC1,Br + C1, = 2CC4 + Br, . 2CC1,Br + 0, = 2COC1, i- Br, + C1, Author.Bodenstein (2. physik. Bodensttin (foc. cit.) Noddack (2. Elektrochem., Noddack (roc. cit.) Warburg (2. Elektrochem, Volmer (Compt. rend., Bowen (your. Chem. SOC., Bowen (your. Chent. SOL, Griiss ( Z . Elektrochem, Griiss (lor. cit.) Chem., 1913, 85, 229) I921,2 9 859) I920,6 54) 19249 178,697) 1923, 123, 1199) 1923,1239 2328) 1923,299 144) Molecules per Quanta. 1 0.96 (2070 tf) I I (Preliminary experiment) I I From Tables I. and 11. it will be seen that the law is applicable only to a few cases, but it breaks down in a large number of cases. I t is now generally held that the light energy is responsible only for the primary change in a photochemical reaction. The subsequent course of the reaction depends on several factors such as the heat energy evolved during the primary process, the radiations received from the light source and the phase conditions of the molecules involved.The thermodynamic proof of Einstein’s law rests on the conception of an ideal perfectly reversible photochemical reaction. Of course, to realise 489490 EINSTEIN'S LAW OF PHOTOCHEMICAL EQUIVALENCE Reaction. Anthracene 3 Dianthracene . . C,H,NO COOH H 2 + C12=2HCl. . . 203+3C2 . . . . . CH,COCH, + H,O = CH, -t CH,. COOH Decomposition of hydrogen peroxide Oxidation of quinine . . . Br + C,H, = HBr + C H Br . Photolysis of hydrogen io6de . Photolysis of hydrogen bromide . Ozone decomposition in He . . Decomposition of ammonia . . Decomposition of aqueous KN 0: . Fumaric +, maleic acid . . Maleic -> fumaric acid .. Decomposition of silver bromide emulsions on photographic plates . . . . . Potassium oxalate and iodine , Ferrous sulphate and iodine . . Sodium nitrite and iodine . . Potassium formate and iodine . Calcium lactate and bromine . 0 - CSH NOZCHO + co I- c1, = COCl, . . . Auto-oxidation of benzaldehyde . N%S03 + 0 = N% - SO, . . Bromine and tartaric acid . . Bromine and cinnamic acid . . Transformation of allocinnamyli- dene acetic acid +. normal form . . . . . Photo-decomposition of potassium permanganate . . . Decomposition of NC1, . . . Decomposition of nitrosyl chloride Decomposition of solution of oxalic acid in presence of uranyl nitrate . . . . . Bromine and stilbene . . . TABLE 11. -______ Author. Bodenstein (Z. physik. Chem., 1913, 85, 229) ,7 9 9 9 , 1 , 9 , ,, 9' 9 , Y ? 7 3 ,¶ 1 9 9 9 9 , 9 Wariurg (Z.'klektri:hem, 1920, 26, 54) 3 , 3 , Y, 7, 1 , I , ,> $ 9 9' Y , 9 9 9 9 1 9 *, Y Y 9 , 7 , , 9 Eggert and Noddack (Sitzs.Preuss. Akad. Wiss., Berlin, 1921, 631) Mukerji and Dhar 9 , Y Y 9 , 9 9 9 ) 9 , 7 9 9 , Gh&h and Basu (Private communication) Backstrom (Taylor's Phjs. Chem., p. 1241) Ghosh and Mukherji (Private communication) Ghosh and Purkayastha Ghosh and Gupta (Private Rideal and Norrish (Proc. Bowen (Joiir. Chenr. Soc., Bowen and Sharp (Jour. Chcm. Soc., 1925, 17, 1026) Boll (Compf. rend., 1913, 3hosh and Purkayastha communication) ROJI. SOC., 1923, 103, 342) 1923, 123,1199) 156, 1891) . _ ~ _ _ _ _ _. Molecules per Quanta. 0-25 1-0'33 'I1 100- 1000 106 200 I00 1-200 I 0 0 106 2 > - 0.85 (A = 2530 A) 0.23 0.25 0.03 0'1 I 3-01 (A = 4078 A) 0'032 0'063 0.026 I0 Many molecules re- act for each energy quanta Many molecules re- act for each energy quanta absorbed 9, 4-12 436 0'5 0.27- I * 18 1.5 (4480 A-5000 A) Less than I 305 practically the ideal condition is an impossibility and hence it is not for us to expect the photoequivalence law to hold in every case.I t is to be observed that most of the reactions in which Einstein's lau- breaks down are exothermic in nature as already remarked in a previous paper. The large amount of energy liberated in these exothermic reactions undoubtedly makes them too complicated for the simple law of photo-PROFESSOR N. R. DHAR AND B. K. MUKERJI 491 chemical equivalence to hold. It seems reasonable that Einstein’s law of photo-equivalence would be more readily applicable to endothermic reactions than to exothermic ones, because in endothermic reactions the light energy absorbed will be utilised wholly or mainly in bringing about the chemical transformation.This statement seems to be borne out by the fact that the reactions in which Einstein’s law holds (Table I.) are mostly endothermic in nature.l Again, Einstein’s expression Q = ~ z h is valid only for one particular wave-length. But, not only light of a definite wave-length can bring about activation but also a band which consists of light .Bf several wave-lengths is usually employed as the light source. From the Bohr point of view it seems likely that only one frequency at a time can bring about activation in a particular case.I t follows therefore, that when the strictest regard is not paid in selecting only the appropriate wave-length the attempt to apply Einstein’s law to a photochemical reaction is not expected to be a success. The filndamental simplicity of Einstein’s law can be fully realised if we restrict our attention only to the primary change in a reaction; but as a matter of fact there is reason to believe that a whole series of frequencies can activate a reaction and this tends to prove the formation of intermediate stages in a reaction, each of which only after the absorption of its char- acteristic frequency would pass to the next stage in the reaction. In order to explain the abnormally large photochemical yield in such exothermal reactions as the combination of hydrogen and chlorine, decompositions of hydrogen peroxide, ozone, etc., we suggest the following explanation based on the emission of ions and electrons in chemical changes :- I t is well known that ions are generated in the combination of oxygen and phosphorus, Similarly Richardson 2 has shown that when metals like Nay K, or alloys of these metals combined with Cl,, COCl, etc., ions are given out.Basing on these facts, we suggest the following mechanism of the combination of chlorine and hydrogen in presence of light. When a mixture of chlorine and hydrogen is illuminated, the chlorine molecule is converted into the active condition by the absorption of light. The activated chlorine molecules can now react with hydrogen molecules. This exothermic chemical change gives out radiation and high moving electrons.These electrons would in their turn activate further molecules of chlorine and these activated chlorine molecules would furthur combine with molecules of hydrogen and this process would continue ; Cl, + hvo = C1, (active) Electron + C1, = C1, (active). C1, (active) + H, = zHC1 + electron + heat energy A similar line of argument can be advanced in explaining the abnormalIy large yield in the photodecomposition of hydrogen peroxide, ozone etc. As has previously been observed in a foregoing paper we can explain the cases of poor photochemical yield as follows : since it has been postu- lated that photochemical changes take place by the formation of activated molecules by the radiant light energy it may be observed that all the collisions of the activated constituent with the rest of the inactive molecules may not be effective in bringing about the chemical change, and by ineffec- tive collision the activated molecule loses its extra amount of energy ’Compare Baly and Barker, your*.Cliem. SOC., 1921, 11% 653. 2 Plzil. Trans., 1921, 222, A, I.492 EINSTEIN’S LAM’ OF PHOTOCHEMICAL EQUIVALENCE and reverts to the inactive state. Hence, the total energy supplied to the system does not wholly contribute to the chemical transformation ; some of the energy being dissipitated to the surroundings. I t is interesting indeed, that a low degree of energy utilisation is characteristic not only of photo- chemical reactions but of chemical changes induced by a-rays and X-rays. Warburg explains poor photochemical yield on the assumption of a primary splitting into atoms which would require much more energy t.han would be represented by the net result of the reaction after their recombina- tion to form new molecules.But it is- extremely doubtful whether a primary splitting up of atoms is at all necessary for a photochemical reaction to proceed. I t must be emphasised at this stage that in all cases the energy level of the activation of atoms and molecules need not exactly correspond with the resonance or ionisation potential of the molecule or the atom concerned. In this connection a recent work by Rideal and Williams’ on the inter- action of ferrous ion and iodine would be of interest. The above authors conclude from their experiment: that the reaction is unimolecular with respect to iodine and h = 5790 A is effective in this change and this wave- length corresponds to 2.14 volts.They have further remarked that this value is practically equal to the resonance potential of iodine molecule (2.34 & - 2 volts) as given in Foote and Mohler’s “Origin of Spectra” page 67. These conclusions of the above authors are doubtful as will be shown from the following facts :- I n a foregoing paper we have shown that the reaction between ferrous sulphate and iodine in light is semi-molecular with respect to iodine. 111 other words, iodine in the atomic condition is reactive in this change. Moreover, from our present knowledge on ionisation and resonance potentials we conclude that these values are really concerned with the elements in the atomic conditions and not in the molecular state.We are of the opinion that the energy in the activated condition should be slightly less than the corresponding resonance potential of the active element in question and this is corroborated by the experimental results obtained in the reaction between iodine and ferrous sulphate in which it will be noted that the resonance potential of iodine atoms and not molecules as assumed by Rideal and Williams has the value 2-34 volts and the activation potential has the value 2.14. I t seems remarkable, however, that investigators in this line with all shades of opinion hardly ever question the soundness of Einstein’s law. The law states that each single molecule of a photo-sensitive substance requires just one quantum h,, of the requisite frequency v0 in order that it may be decomposed. On the Hohr theory, however, the absorption of a single quantum of every htv, signifies simply the interorbital transition of an electron inside the atom. Thus, of course, one can easily conceive that by the absorption of a quantum of‘ energy of the requisite magnitude an atom may be decomposed. As a logical consequence of this Einstein’s law is easily comprehensible in cases of monatomic molecules but when, say, diatomic molecules are involved this law obviously loses much of its significance. The present stage of our physical knowledge about molecules does not warrant us to attribute the decomposition of molecules as well to the simple interorbital transition of an electron. lyour. CIICIJZ. SOL., 192j, 127, 25s.PROFESSOR N. R. DHAR AND B. K. MUKERJI 493 Summary. (i) From a survey of the experimental results hitherto obtained, it is found that Einstein’s law of photoequivalence breaks down in the majority of cases. (ii) In our opinion Einstein’s law should be more applicable to endothermic reactions -than to exothermic ones. (iii) The abnormally large yield obtained in the photochemical combina- tion of hydrogen and chlorine has been explained from the point of view of electron emission during the interaction of activated chlorine molecules with hydrogen to form hydrochloric acid. The electrons thus emitted further activate more chlorine molecules and as such supplements tbe effect of light as a source of activation. Chemicn Z Laboratory, Alluhbad Uainersity, Adzahbad (India), August 3 ~ d , 1925.

ISSN:0014-7672    

DOI:10.1039/TF9262100489

出版商:RSC    

年代:1926

数据来源: RSC