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. The Fnraday Society is not responsible f o r opiniom expressed before it by Authors or Speakers. aransactions OF Cbe garabay Society. FOUNDED I 903. T O PROMOTE THE STUDY OF ELECTROCHEMISTRY, ELECTROMETALLURGY, CHEMICAL PHYSICS, METALLOGRAPHY, AND KINDRED SUBJECTS. VOL. xx. AUGUST, I 924. PART I. SUGGESTIONS FOR A MAGNETIC THEORY OF VALENCY. BY PRINCIPAL A. P. LAURIE, M.A., D.Sc. ( A paper read before THE FARADAY SOCIETY, MOnda,Y, february 18th, 1924, SIR ROBERT ROBERTSON, K.B.E., F.R.S., PRESIDENT, in the Chair.) (MS. received February I 8 th, I g 2 4.) In a paper read before the Royal Society of Edinburgh I suggested a theory of valency based upon two assumptions, namely that the electrons are arranged round the nucleus in a series of rings or shells as shown in the Langmuir atom, and that the electrons themselves are moving in tiny orbits which we shall assume to be of much smaller diameter than the diameter of the atom. The atom is supposed to be drawn in one plane with the tiny orbits of the electrons at right angles to the plane and in- serted radially round the nucleus so that we can represent them in plan as a short straight line, with a north and south magnetic face on each side respectively. We may for convenience call these units magnetons. The justification for the assumption made will be given later on.I n the fol- lowing paper I propose to extend this view of chemical combination to fresh cases. The Combination of Ions. In the former paper, I showed that a study of the magnetic field be- tween two such approaching atoms made it probable that, in the case of two non-metallic elements, the combination between the atoms took place as shown in Fig. I , two of the magnetons moving out in the magnetic field; and that, if we supposed in the non-metallic elements, that the outer shell of magnetons were inserted round the nucleus with the poles in one direction, and in the metallic elements in the opposite direction, then a magnetic field would be produced which would tend to draw the two magnetons opposite to each other into the position shown in Fig.2, 1 L L Experiments with a Model to illustrate the combination of two atoms consisting of Magnetons round a Positive Nucle‘us,” by A. P. Laurie, Vol. XLIII., Part I. (No. 5)- I2 SUGGESTIONS FOR A MAGNETIC THEORY OF VALENCY and we might then suppose the two being drawn into the shell with the strongest magnetic field. If we take as an example chlorine and sodium the following figures (3) and (4) illustrate this transference of a magneton from the one atom to the other. I 1 I w 0 0 - 1 I FIG. I. I + 4. FIG. 2. But the transference having taken place, we now have the magnetons in the outer shell of the chlorine ion facing the magnetons in the inner shell of the sodium ion, and it seems reasonable to suppose, in order to get a stable magnetic structure, that if the outer shell of magnetons in anSUGGESTIONS FOR A MAGNETIC THEORY OF VALENCY 3 atom are inserted in the order N, S, those in the inner shell will be in- serted in the order S, N.We can now therefore suppose the magnetons in the outer shell of the chlorine ion combining with the inner shell of the magnetons in the sodium ion, as shown in Fig. 5. If this view is correct, the distinction made by Langmuir and others between the two kinds of SODIUM FIG. 3. SODIUM FIG. 4. Is CHLORIME 4 5 FIG. 5.-These diagrams show the upper half of the atoms. The other four mag- netons are supposed to be on the lower half. chemical combination, one the transference of electrons, and the other, the sharing of electrons between two atoms requires modification.According to my hypothesis, the combination between two non-metallic elements involves the sharing of magnetons as in the Langmuir hypothesis. But in the case of a non-metallic element combining with a metallic4 SUGGESTIONS FOR A MAGNETIC THEORY OF VALENCY element, the transference of one or more magnetons is followed by the combination of the non-metallic with the inner shell of the metallic element. This view of chemical combination is in general agreement with what we know of the arrangement of atoms and ions inside a crystal. If, for example, we take the sodium chloride crystal, the alternate arrangement of sodium and chlorine ions will be conditioned as pointed out by Sir W. H. Bragg by their + ve and - ve charges. If we then consider these ions from the point of view of their external magnetons, they each have eight, and will be able to combine indifferently with themselves or each other.Owing to their primary and secondary valencies one ion can combine with eight other ions, distributed four and four on two diagonal planes to the cubic formation. These eight again form fresh centres of combination and so the crystal is built up. Lithium chloride, it may be pointed out, is difficult to explain on this assumption. Moreover the above suggestions as to the nature of the combination between sodium and chlorine seem to reconcile the fact that ionisation of sodium and chlorine has already taken place in the crystal, with the known facts of solution of the salt in water. If we imagine the sodium and chlorine ions passing into solution, they would be magnetically attracted and tend to form molecular groups, except in so far as they were separated from each other by the hydration of the respective ions, and for any given strength of solution we would have an equilibrium set up between the number of the ions combined with each other, and the number of separated hydrated ions, thus agreeing with the old hypothesis of ionisation on dilution.Water Polymerides and Hydrates. This brings me to the second part of my paper, the formation of poly- merides of the water molecule and of hydrates. In the diagram illustrating the formation of hydrates no attempt is made to draw figures which repre- sent the relative distances of the atoms from each other. We may assume the distances between the water molecules in a water hydrate being suffi- ciently large to admit the introduction of an ion or molecular group into the ring.If we suppose three in the upper half and three in the lower half of the atom, then we can represent the combination of the upper half of the atoms in one plane, the figure being repeated for the lower half. I f we suppose three atoms of oxygen combining together we should get according to our theory the following distribution of magnetons for the upper halfs of the atoms (Fig. 6). The magnetons a, a, a, are internal “bound ” magnetons and cannot take part in any further combinations formed by the molecular group. The inagnetons b, b, b, are external “bound ’’ magnetons. They can assist in combination by forming a magnetic field but cannot readily move out from their position.The magnetons c, c, c, are “free ” magnetons which can move out into new positions forming compounds with other atoms. The distinction between internal and external bound magnetons is more clearly shown if we represent the atoms as circles touching each other and introduce the magnetons into the spaces between the atoms. Let us now attach three hydrogen atoms to this group of oxygen atoms and make the assumption that the molecule arranges itself so as to be as compact as possible. The result is shown in Fig. 7. Let us suppose three hydrogen atoms attached to the lower half of this group of oxygen atoms in the same way and we have a figure representing the polymeride 3H,O. The peculiarity about this polymeride is that it con- The oxygen atom has six external magnetons.SUGGESTIONS FOR A MAGNETIC THEORY OF VALENCY 5 tains no external magnetons, and therefore cannot enter into any further chemical combination unless it is broken up by a sufficiently strong mag- netic field into its original molecules.If we suppose a larger number of I C FIG. 6.6 SUGGESTIONS FOR A MAGNETIC THEORY OF VALENCY water molecules uniting to form a polymeride we get a series of rings, or hollow shells if arranged in three dimensions, none of which has any FIG. 8. external magnetons, Fig. 8. This arrangement of molecules in groups of three is not incompatible with the grouping of atoms in ice as shown by Sir W. H. Bragg. FIG. 9.-The circles represent oxygen atoms. The hydrogen atoms have been left out.Sir W. H. Bragg has shown that in the ice crystal the oxygen atoms are arranged in tetrahedra which are connected together so as to leave a hexagonal spacing, a hydrogen atom being placed between each two oxygen atoms in the tetrahedron. This arrangement can apparently be derived from the tri-hydrate as figured, if we suppose that the external hydrogenSUGGESTIONS FOR A MAGNETIC THEORY OF VALENCY 7 atoms are able to rearrange themselves so as to connect the trihydrates together into an hexagonal pattern, and that the trihydrates are arranged as shown in Fig. g with spaces between them, the trihydrate triangles, composed of oxygen atoms, sloping like slats of a ventilator as shown in the diagram, and the bases of the triangles drawn out. Let us now proceed to consider the formation of the hydrate of an ion, and let us in the first instance assume that the ion has six external free magnetons.The lowest water hydrate with no external magnetons is 3H,O, and we shall now place an ion in the middle of the ring of the water hydrate drawing the arrangement of the magnetons in the upper plane, Fig. 10. The ion is supposed to have six external magnetons and to attach to itself three water molecules. The total number of magnetons utilised is 12 + 3, and the same number will be utilised in the lower plane. This hydrate has no external magnetons and therefore may be regarded as chemically neutral to a water hydrate. Among other properties we should expect such a system of ion FIQ. 10.-Hydrate of ion with three external magnetons. hydrates to have the same viscosity as the water hydrates with which they were mixed.But it has an additional property. If the diagrams for the water hydrates are examined it will be noticed that each oxygen atom, and therefore each water molecule, is held in the ring by a magnetic field pro- duced by four magnetons on each plane. If the diagram for the ion hydrate is examined it will also be found that though three magnetons have been added to the complex molecule on each plane, each oxygen atom is still only held by four magnetons on each plane. So that as a first approximation we can say that the magnetic field holding a water molecule in the complex is the same for the water hydrate as for an ionic hydrate and, therefore, water molecules can be exchanged between the two without any loss or gain of energy.If we next suppose an ion with three external magnetons we can suppose the three utilised in one plane and again there will be on both planes four magnetons to each oxygen atom. In order therefore to form what I venture to call perfect hydrates, we require for ions with 3, or 6 external magnetons, three water molecules, for 4 or 8, four water molecules and so on.8 SUGGESTIONS FOR A MAGNETIC THEORY OF VALENCY Doubtless there are intermediate hydrates, but only these perfect hydrates fulfil the conditions necessary if dilute solutions are to obey the gas laws. So far we have not considered ions with less than three external magnetons. The hydrogen ion with none will, I imagine, not form a hydra tea1 If we assume that the lowest perfect water hydrate contains three molecules of water and place the lithium ion in the middle, Fig.12, we find that while The next ion to be considered is the lithium ion with two. FIG. xI.-Ion with eight magnetons and four molecules of water. one oxygen atom is held by four magnetons, one is held by five, and the other by three, thus not forming a symmetrical complex. If we assume, on the other hand, that the lithium ion combines with two water molecules, we have then some of the external magnetons not utilised. These irregularities may possibly explain the high viscosity value for lithiurn chloride. Finally it may be pointed out that the theory of hydration here de- veloped agrees with the results obtained by Sackurx who, on applying the van der Waals equation to the osmotic pressure of solutions of water, found that up to considerable concentrations the simplified equation P(V - 8) = R .T applies with considerable accuracy, that is, the factor -5 which is due to the attraction of the molecules for each other can be VJ ignored except in very concentrated solutions. If the above theory of hydration is correct, there would be no “ chemical ” or electromagnetic attraction between the water and ionic hydrates. They would, of course, differ from unionised molecules in this, that the ionic hydrates would have + ve and - ve changes respectively. Connection between the Langmuir and the Bohr Atom. If we assume the method of combination between two Langmuir atoms described in this paper we can easily p a s fmm a Langmuir molecule to a molecule of the Bohr type.with no ‘‘ external free ” magnetons. If we suppose two protons united to one water molecule we would get a complex March 4th. 2Zeitsch. physik. Chew., 70, 477, 1910.SUGGESTIONS FOR A MAGNETIC THEORY OF VALENCY 9 G. C. Evans1 has investigated mathematically a transformation of a Bohr into a Langmuir atom and has shown that the Langmuir atom is equivalent to the Bohr atom with a circular orbit. FIG. 12.-Lithium hydrate. We can arrive at this result in another way. So far we have imagined the magnetons taking up fixed positions in space, but if we again examine the water molecule there is another possibility. The water molecule can 0 I I I I I 0 I 1 FIG. 13. be represented as follows according to the theory developed in this paper, bringing the hydrogen nuclei both on the same plane, Fig.13. 1 Bohr-Langmuir Transformation, by G. C. Evans. “ Proceeding of the National Academy of Sciences of the United States of America,” Vol. IX., No. 7, p. 230.10 SUGGESTIONS FOR A MAGNETlC THEORY OF VALENCY Let us now suppose that instead of remaining stationary these magnetons are rotating in three parallel circles at right angles to the plane of the paper, two between each of the oxygen and hydrogen nuclei, and four round the oxygen atom, leaving two internal magnetons in the oxygen atom according to Langmuir, which I have not figured. I t is evident that we have here a molecule closely resembling the water molecule suggested by Bohr, and at the same time if the magnetons keep in step one with another, fulfilling the conditions required by my suggested method of combination of the Langmuir atom.We have thus passed from the statical atom to a molecule of the Bohr type though not exactly the same, as Bohr places three electrons between each of the nuclei and the remaining four rotating round the oxygen atom. In fact the water mole- cule figured by me is a plan of a Bohr water molecule on a plane passing through the orbits of the Bohr molecule at right angles to the orbits of the electrons. We can now take another step. We have assumed the electrons moving in small orbits to produce a magnetic field. We can now replace these small orbits by the orbit of the electron itself, as we can regard the electron, because of its motion, carrying an electromagnetic field with itself, and at any point in its orbit replaced by a short length of an electric current or a tiny flat magnet.This is in agreement with Bohr’s descrip- tion of the way in which two hydrogen ions combine to form a molecule of hydrogen, the initiation of chemical combination being due to the electromagnetic attraction between the electrons due to their motion. This seems to justify the using of this convenient statical method to study chemical combination. I n the case of the water molecule, the magnetic lines of force run round the molecule at right angles to the circles of motion and the strength of the field remains uniform. This uniformity of field is not true of most cases when more than two atoms are combined. If, for instance, we examine the cases of the oxygen molecule and ozone, the two atoms of the oxygen molecule will be held together by two or four magnetons which, if rotating in a circle, can be supposed to do so in step with the magnetons rotating round each of the oxygen atoms. But if we imagine three oxygen atoms united together with three pairs of magnetons, rotating in three circles, the axes of which are 1 2 0 O to each other, it is evident that the strength of the circular magnetic field passing through the three magnetons will vary and that, therefore, the strength of the bond holding the three atoms together will pulsate from a maximum to a minimum, and that con- sequently another magnetic field approaching this molecular group at the right time, could easily remove an oxygen atom, thus accounting for the instability of ozone. The assumption of pulsating magnetic fields of force, holding atoms together in combination, opens up new possibilities of ex- plaining the interchange between atoms when present in solution, and many other chemical phenomena. In the case of the molecules of a gas where two atoms are combined, and of the carbon chain, and of acetylene, and of water, we can suppose magnetic fields which are not varying in strength thus accounting for the fact that atoms in a gaseous form when stable are in groups of two, and for the resistance to chemical change of the carbon chain, and the stability of such bodies as water and acetylene.

ISSN:0014-7672    

DOI:10.1039/TF9242000001

出版商:RSC    

年代:1924

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. DISCUSSION I 1 DISCUSSION. Professor Alfred W. Porter said that not having had the opportunity to see the paper before the meeting, what Principal Laurie had said came to him as rather a novel series of suggestions. With the need for re- cognising magnetic forces in the atom he fully agreed. The great weakness of the Bohr theory was the neglect of the magnetic side of the atom, although there was strong evidedce that it existed. A second weakness of the Bohr theory was that it is exceedingly difficult to conceive of the atom being an equilibrium system (or at least of a group of atoms forming an equilibrium system) when the electrons which play such an important part change in position from moment to moment.We could understand the theory better if the orbits were supposed to be stationary orbits, but that was not the supposition that Bohr had made. Therefore, it was exceedingly difficult to understand, on any principle of mechanics, how a system like that of Bohr could possibly be one which would remain in stable equilibrium. There was also evidence that the magnetic elements are small, and that had also been one of the fundamental assumptions made by Principal Laurie. The work that Oxley had done sufficiently showed the importance of these small stationary elements.On the other hand, if it is wrong to neglect the magnetic side, as Bohr does, it should be equally wrong to neglect the electric side, as Principal Laurie has done. There were two systems of forces present in the molecule, and he defied anyone to work out, on mechanical lines, the stability of a proposed atom unless both were taken into account. He would like to point out that in the actual model shown, the equilibrium was in part maintained by the wovden framework and not wholly by magnetic forces. If these wooden supports were removed, what were the magnetic orbits going to do ? The rigid framework completely altered the conditions of equilibrium. With regard to the actual success of the suppositions made by Principal Laurie in co-ordinating the various facts of chemical combination, it was impossible to estimate without further consideration.Perhaps, when he had had a chance of reading the paper he would be able to form a more definite conclusion. At the present time he would assert only that in his opinion all suggestions ought to be welcomed in regard to this matter because he did not think we were yet anywhere near finality concerning it. Dr. B. Flurscheim said that in view of the remarkable success achieved by the Bohr theory Principal Laurie’s attempt to connect this theory with the chemical properties of the atom appeared to be very interesting. Electrostatic theories of chemical combination had hitherto failed to account satisfactorily for the alternation of forces in organic chains.The introduction of a substituent caused an alternating increase and decrease in the amount of chemical force used up in successive bonds in a chain. This was evidenced by thousands of facts, and was recognised more and more by organic chemists. If Principal Laurie’s magnetic theory of chemical combination could account for these facts, then it would constitute a distinct advance. The President said he thought Professor Porter was right when he said that all suggestions should be welcomed and he was sure all those present had listened with much interest to the fascinating account which Principal Laurie had given, although there had not been time to study it. I t should be appropriate for the Faraday Society, bearing the name of such a founder, to learn of further examples of the connection between Could it account for them?12 SUGGESTIONS FOR A MAGNETIC THEORY OF VALENCY magnetism and rotation.These magnetic phenomena are now being taken into account by those who are considering the structure of the atom. H e had noticed recently a reference to experiments by Stern and Gerlack 1 who projected atomic silver through a non-uniform magnetic field on to a glass plate, and found that there were two spots of silver on the plate instead of one. This deflection they found to be due to the atom of silver possessing a magnetic moment, which sets itself parallel to or anti- parallel to the magnetic field, i.e. the two moments are at right angles to one another.If this is the case with the silver atom, it is very probable that the same thing will be found to hold with the atoms of other elements. Principal Laurie, in replying to the comments that had been made, said that it must not be assumed that he was ignoring the presence of the electrostatic forces because he had emphasised the importance of the magnetic forces in explaining chemical combination. Professor Porter would realise that it would be necessary in considering both these forces to give the right values to each of them, and he had felt that any attempt to do that at our present stage of knowledge would lead one into serious difficulties. H e had, therefore, preferred to treat the matter qualitatively and avoid all attempt at quantitative calculations which would involve the consideration of the electrostatic as well as the electro-magnetic forces.Professor Porter : Are they not equally in balance with one another? Principal Laurie continuing said that probably the electrostatic forces were varying as the inverse square of the distance and the magnetic forces as the inverse of the fourth power of the distance, consequently, their relative importance would change rapidly according to the distance between the atoms. What Professor Porter had said was probably true if it were assumed that the electrons were moving in circles between the nuclei of the atoms in combination as he had shown from his diagrams and models. If the electrons are moving in circles between the nuclei the result must be to produce a varying magnetic field which would mean that at one instant the atoms were held together much more strongly than at another instant. Such a view of the varying force of attraction would do much to explain the interchanges taking place when salts were present together in solution and to give the final explanation of this equilibrium of interchange which was known as the law of mass action. There was another possibility introduced by this view of a varying magnetic field and that was that in order for two atoms to combine the two vibrating magnetic fields must be in tune one with the other. This might explain one of the most curious facts which was constantly present to the chemist and that was the selective character of chemical combination. Zeit. Physik, 7, 85 (1921) ; 9, 345, 353 (1922) ; Physicu, 2, 122 (1922).

ISSN:0014-7672    

DOI:10.1039/TF9242000011

出版商:RSC    

年代:1924

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. THE ELECTRONIC THEORY OF VALENCY. PART IV. THE ORIGIN OF ACIDITY. BY PROFESSOR T. MARTIN LOWRY, C.B.E., M.A., D.Sc., F.R.S. (A paper read before THE FARADA4Y SOCIETY, Monday, I;’ebruary I 8th, I 924, SIR ROBERT ROBERTSON, K.B.E., F.R.S., PRESIDENT, in the Chuir.) ReceivedJutzuary 2 st, I 924.The object of this communication is to unite into one definite hypo- thesis a number of suggestions which have been made in earlier papers of this series, and elsewhere, as to the nature of acids and the origin of acidity. I. The Nature of Acids. An acid may be defined as a hydride from which a proton can be detached, e.g., on dissolution in an ionising solvent, on electrolysis, or by displace- ment by a metallic ion. appears likely to hold its own, in spite of proposals that would either restrict its scope,% by limiting it to the hydrates of anhydro-acids,3 or broaden it to include compounds not containing any hydr~gen.~ Thus, although it is true that water is needed to make hydrogen chloride conduct, this does not prove that water is a necessary constituent of an acid, since it may only mean that the proton always seeks out an alternative resting-place when it is threatened with eviction from an acid, and that if alternative accommodation is not provided, it may refuse to be displaced.In other words, the ionisation of an acid may be, not a dissociation as expressed in such an equation as This definition + - + - H C l e H + C1 or HClaq =+ Haq + Claq but a double decomposition of the type + + HC1+ OH,--,OH, + el compare HCl + NH,+NH, + el There is therefore no need to narrow the definition of an acid by confining it to compounds which contain oxygen as well as hydrogen. On the other hand, there are real advantages in maintaining the positive relationship between acidity and the presence of a proton which is indicated in the definition set out above, in place of widening this definition so as to include any substance which can make away with a hydroxyl ion, or even with another anion, such as fluorine.1 Cf. Chemistry and Industry, 1923, 42, 43. 3 Werner, New Ideas, 1911, p. 212 ; cf. Chemistry and Industry, 1923, 42, p. 1048. 4G. N. Lewis, Valence, 1923, p. 142. 216id., p. 46. I3THE ELECTRONIC THEORY OF VALENCY 2 . The Development of Acidi'ty. When the hydrides of the lighter elements are compared, a very remarkable contrast is observed between successive members of a series such as CH4, NH,, OH?, FH, Ne. Thus the monohydrides, FH, ClH, BrH, IH, are amongst the strongest acids; but SH2 is already a very weak acid and OH2 is commonly regarded as neutral.Ammonia is more of a base than an acid, since it is more ready to take up a proton as in t - + - NH4CI than to lose one as in NaNH2. I n methane, acidic and basic properties have both disappeared, the former on account of the greater stability of this hydride as compared with NH, or OH,, the latter, on account of the fact that the octet of carbon cannot carry any more radicals beyond the four hydrogen atoms which are already attached to it in methane. I n the first paper of this series,' I suggested that this progressive disappear- ance of acidity was not due directly to a change of valency, but that it might be associated much more closely with the growing size of the mole- cule which had been demonstrated by the experiments of Rankine2 on the collision-areas of these molecules as deduced from measurements of the viscosity of the gases.This suggestion is repeated in a more precise form in the following paragraph. 3. Although the brilliant investigations of Bohr have led at present only to a theory of the structure of free atoms and ions, it is already possible to surmise the direction in which developments must take place in order that it may provide in due course a working hypothesis of the structure of molecules also. I n particular, the view is now widely accepted that the '' shared electrons " of the static models must be translated into 'L shared orbits " 3 in the dynamic model of the molecule. In the recent discussion on '' The Electronic Theory of Valency," I suggested that the develop- ment of looped orbits may be related in a very simple manner to the well-known relativity effect.I n a free atom or ion this gives rise to pre- cession of the orbit ; but the intersection of the inward and outward paths, which is the main feature of this effect, is exactly what is needed in order to produce a figure-of-eight orbit enveloping two nuclei. Since the major axis of an orbit is inversely proportional to the effective nuclear charge, it is clear that the size of the loop must be smaller in FH with a nuclear charge of g than in CH, with a nuclear charge of 6, in complete qualitative agreement with the observations of Rankine. I t is not easy to say what relationship will exist between the size of the looped orbit and the magnitude of the force with which it binds together the two nuclei which it encloses ; but the repulsion between them must certainly increase rapidly as the two nuclei are brought more closely together by the contrac- tion of the loop.From this point of view it appears that the four hydrogens of methane may be held securely by looped orbits, with the focus of the outer loops at a considerable distance from the nucleus, whereas the much smaller loop in which the proton of hydrogen fluoride is held must bring it nearer to the nucleus, and may easily bring it so near that it can be driven outside the loop by the strong repulsion to which it is subjected. BOWS Atom in Relation to the Problem of Acidity. 1 Trans. Faraday SOL., 1923, 18, p. 292 ; Phil. Mag., 1923, 45, p. 1116. 2 Trans. Faraday SOL., 1922, 17, 719.3 Niessen, Dissertutiorr, Utrecht, 1922, Pauli, A m . d. Physik, 1922, 68, 177 ; Camp- bell, Nature, April 28,1923, 111 ; Fowler, Trans. Faraday SOC., 1g23,19,461; Sidgwick ibid., p. 469. Trans. Faradaj, soc., 1923, 19, 480.PART IV. THE ORIGIN OF ACIDITY I5 4. Transmission of Acidify. I t is of interest to reconsider, in the light of the views set out in the preceding paragraph, the mechanism by which acidity is propagated in a chain of atoms, e.g., from C1 to H in C1. CH, , CO. OH. When a static model is used, the simplest mechanism is that suggested by Langmuir,l namely a displacement of the nuclei relatively to the enveloping shells of electrons. When a dynamic model is used, this conception becomes of less utility, since it is difficult to imagine that the orbits can be diverted very much from their normal course round the nucleus, at any rate in the inner portion of the path. I t is therefore more reasonable to suppose that, since an orbit with a chlorine-nucleus in one focus is necessarily of smaller dimensions than a corresponding orbit containing a carbon nucleus, the dimensions of a looped orbit which contains chlorine in one focus and carbon in the other, will be intermediate in size between those of binuclear orbits containing either two chlorine or two carbon atoms.I t is moreover reasonable to think that the contracted orbits of a chlorine atom may tend to impose a like contraction on orbits of similar quantum-number in an adjacent carbon atom when some of these orbits are shared by both atoms.This effect, transmitted in a diminished degree as the length of the chain is increased, would account for the general effect of acylous and basylous radicals as illustrated by the tables in Part III. of this series of papers. I t will be noticed that this effect is uniform in character throughout. I t has been suggested that, in the transmission of acidity through a chain of atoms, an alternating effect (basylous, acylous, basylous, acylous, etc.) is sometimes produced in consecutive atoms; but, as I have already stated, I am not yet convinced that there is any sufficient experimental basis for this view. 5 . Summary and Condusions. (a) The increasing acidity of the hydrides from CH, to FH or from SiH4 to C1H is attributed to a progressive diminution in the size of the orbits of the electrons by which the protons are linked to the central nucleus. (b) I t is suggested that acylous atoms such as chlorine tend to diminish the size of the orbits of electrons which they share with another atom, and that this effect can be transmitted to other orbits of the same quantum- number in the latter atom. In this way the transmission of acidity through a chain of atoms can be interpreted by means of a dynamic, instead of a static, model. Conversely, basylous groups must expand the orbits of electrons which they share with other atoms. (c) From this point of view an unsubstituted hydrocarbon chain should act as a neutral radical in carboxylic acids, since orbits shared by two carbon atoms will be of normal dimensions. Hydrogen directly attached to an atom of sulphur, phosphorus, etc., is more acylous than an alkyl radical because it allows for a greater contraction of the orbits; but even a proton is less acylous than the " lone pairs " of electrons in acids such as FH and ClH, since contraction is probably at a maximum in orbits which are entirely unshared. 1 Trans. Faraday SOC., 1922, 17, 609.

ISSN:0014-7672    

DOI:10.1039/TF9242000013

出版商:RSC    

年代:1924

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. 16 THE ELECTRONIC THEORY OF VALENCY DISCUSSIOA? Principal A. P. Laurie said he always thought of the orbits as going round in between the nuclei, Professor Lowry said that used to be the view held but it was not SO now, he believed. Dr. B. Flurscheim said : Chemists cannot afford to ignore the Bohr atom, and it therefore appears necessary to connect the problem of acidity with the Bohr atom. Regarding the particular method of connection now proposed by Professor Lowry, a number of objections present themselves. They relate to matter of common knowledge ; presumably, therefore, Pro- fessor Lowry has considered them before advancing his hypothesis, and will be able to provide an answer.I. According to the Bohr-Sommerfeld theory, the relativity effect causes precession of the electronic orbit in its own plane; the fixed pivot of this movement is the focus occupied by the nucleus. I n Professor Lowry's model, on the contrary, the fixed pivot lies in that part of the orbit which is at greatest distance from the nucleus. The Bohr-Sommerfeld preces- sion is exceedingly slow (for hydrogen maximum abopt 0.01' for one re- volution of the electron), whereas Professor Lowry's figure of 8 involves precession of 180' for one revolution of the electron.2 . It is quite true that the major axes of the Bohr orbits of the outer electrons of fluorine and chlorine are smaller than those of carbon. Pro- fessor Lowry attributes to this difference the fact that hydrogen chloride and fluoride are acids, whereas methane is not. But why not compare iodine? According to Bohrl the major axis of the outer electronic orbits of xenon is only slightly smaller than for carbon, and since it is some- what larger for iodine than for xenon, it must be approximately equal for iodine and carbon. On Professor Lowry's assumption, methane and hydrogen iodide should therefore be acids of about equal strength. Or, taking elements in one and the same period, there is a successive increase in the length of the major axis of the outer electronic orbits as we proceed from oxygen via sulphur and selenium to tellurium.But the dissociation constants of the corresponding hydrides are for H,O = 1.2 x 10-14; H,S = 0.91 x I O - ~ ; H,Se = 1-88 x I O - ~ ; H,Te = 2.27 x I O - ~ . I n other words, whereas hydrogen telluride, for instance, should according to Professor Lowry be a very much weaker acid than water, it is some hundred thousand million times stronger. 3. Professor Lowry admits that the effect which a substituent has on the strength of an acid must, on his assumptions, always be in the same direction, whatever its position. Alternating increase and decrease of the strength of an acid by introducing a substituent in different positions would be excluded, nor is Professor Lowry convinced that there is a suffici- ent experimental basis for it.But this is not a question of conviction, it is one of fact, and alternation is a fact. Thus, in any aliphatic acid, an anilino-group in the a-position raises the strength of the acid, and lowers it in the P-position. A hydroxyl-group in the meta-position raises the strength of benzoic acid, in para it lowers it. Acetoxy- and acetamino-groups do the same. This effect may even be found when the substituting and the ionising groups are far apart. Thus meta-oxy-cinnamic acid is stronger than cinnamic, and para-oxy-cinnamic acid is weaker than cinnamic acid. These are :- 1 Natuvwissensch, 11, 556, [1g23], Table I.DISCUSSION I 7 I have already shown (see the Faraday Society’s “Electronic Theory of Valency,” XIX., p.534) that inner salt formation cannot account for such differences, and I imagine that no one would suggest such an explanation for the oxy-cinnamic acids, which are known to be trans-acids : II and C 0 H/ \,-./ H The above formuk contain the explanation which my own theory sug- gests for the relative ease with which hydrogen dissociates in both cases ; but whether my own particular interpretation may ultimately prove to be right or wrong, the facts which demonstrate alternation will remain, and no theory of acidity which chooses simply to ignore them can advance us much further toward the truth. Professor Lowry in reply to the discussion said he had never denied that alternating polarities exist in unsaturated or conjugated chains or rings, such as are found in aromatic compounds, but his doubt was whether they existed in saturated chains of single bonds. Thus in the series of fatty acids, the influence of a halogen is always of the same character, giving rise invariably to an acylous effect, and he believed that this was a general characteristic of saturated chains. In reply to Dr. Flurscheim’s second paragraph, it was reasonable to make a comparison between orbits belonging to the same sub-group ; but it was not reasonable to extend this comparison, as Dr. Flurscheim had done, in such a way as to cover orbits belonging to different sub-groups, since the influence of the inner electronic systems ought not to be “written off” as negligible.

ISSN:0014-7672    

DOI:10.1039/TF9242000016

出版商:RSC    

年代:1924

数据来源: RSC

摘要:

ON CERTAIN PHYSICAL DIFFERENCES BETWEEN SOLS AND GELS OF AGAR. By E. HATSCHEK and R. H. HUMPHRY. ( A Paper read before the FARADAY SOCIETY, Monday, Feh-unr- 18th, 1924, SIR ROBERT ROBERTSON, K.B.E., F.R.S., PRESIDENT, in the Chair.) Received November 5 th, I 9 2 3. The only comprehensive determinations of various Rhysical constants of the sol and gel of a given substance, at the same temperature, are those carried out by McBain and his collaborators on soap sols and gels.1 The most striking of their results is probably the demonstration that the elec- trical conductivities of sol and gel, at equal concentration and temperature, are identical. The case of soaps, as colloidal electrolytes, is somewhat special, and it appeared of interest to ascertain whether the same result would be ob- tained in sols and gels having a negligible conductivity of their own, but containing a normal electrolyte.Agar sols and gels were chosen for in- vestigation, partly on account of the comparative indifference of the sub- stance, and partly for the wide hysteresis range, which permits the existence of either sol or gel between about 3 5 O and 95" C. The electrolyte used was copper sulphate in moderate concentration. Preparation uf Concentrated Agar Soh.-The preparation of dear sols con- taining as much as 5 and even 7 per cent. of agar fortunately proved to be a much simpler matter than experience of the procedure usually adopted in making I or 2 per cent. sols would have led one to expect. I t was found that sols containing 5 per cent. or more, when kept at 80" C.for two to four hours, became quite clear, the insoluble constituents gradually gathering together into a dirty grey coagulum, which could be retained by a plug of glass wool in a funnel provided with a hot water jacket. This procedure was found so convenient that sols of lower concentration were always made from the clear 5 per cent. sol by dilution. Incidentally it may be remarked that at lower concentrations the amount of insoluble matter is probably insufficient to form a dense coagulum, although even then the sols become much more easily filtrable through paper after being kept at about 80" C. for some hours.2 Sols prepared as described are quite clear in a thickness of 2 5 mm. in transmitted light and show no opalescence whatever in reflected light.During setting, however, the gel becomes remarkably opalescent. Fig. I shows two test tubes, containing sol (left) and gel respectively, which had M. E. Laing and J. W. McRain, Trans. Chem. SOL., Vol. 117, r506 (1920). De Jong, Dissertation Utrecht, " Het Agarsol," 1921. I8FIG. I. FIG. 2. [To facepage 18, VOL. XX-T1-18aA 1 FIG. 3. [To facepage 19.DIFFERENCES BETWEEN SOLS AND GELS OF AGAR 19 been brought to a temperature of 62"in the thermostat, then placed in front of a dark background and photographed as rapidly as possible. Since the gel scatters a considerable amount of light, it appears (though still quite clear) much darker in transmitted light than the corresponding sol. Fig. 2 is a photograph of two test tubes containing sol (left) and gel respectively, photographed in the thermostat at 62' by transmitted light, which exhibits this difference very strikingly.I t may be worth while add- ing, that the opalescence of the gel does not alter perceptibly if it is kept for several days at 62", i.e. at a temperature at which sol can exist and is per- fectly clear in reflected light. This observation appears to dispose of the explanation which most readily suggests itself: that the opalescence is due to segregation of a phase insoluble at or below the setting point (33"-35'), since there seems to be no reason why such a phase should not re-dissolve in a gel kept for prolonged periods at a temperature much above the setting point. The term : 5 per cent. sol means a sol obtained by dispersing 5 gm.of agar in IOO C.C. of water. The water lost by evaporation during dispersion and the subsequent period of clearing at 80" was made up as nearly as possible ; as, however, the coagulum represents an appreciable amount of dry matter, the actual concentrations, as determined by drying to constant weight at 100" C., differ slightly from the nominal values. The values thus obtained are given below, although without bearing on the subject of the present investigation, which was simply the comparison of agar-electrolyte systems in the state of sol and gel. The electrolyte used throughout was copper sulphate, in a concentration of 2 gm. of the crystallised salt to IOO gm. of water (i.e. 2 gm. to 105 gm. of 5 per cent. sol) or approximately M/I 2.5. The sol was allowed to cool to about 80" and the finely powdered salt added in small portions and dis- solved with constant stirring. Conductivity Measuremenfs.-The choice of a suitable conductivity vessel offered some difficulty for the following reasons.The vessel had to be filled with sol containing copper sulphate and the conductivity deter- mined at some temperature well above the setting point. I t had then to be cooled below the setting point and, after complete gelation of the con- tents, warmed to the same temperature at which the conductivity of the sol had been measured. However slowly this was done, the expansion of the gel caused it to detach itself from the copper electrodes which were tried in the first instance, and it was therefore decided to use liquid electrodes capable of taking up the expansion and contraction.The type of vessel finally adopted is illustrated in Fig. 3. I t consists of an inverted U-tube 15 mm. internal diameter, closed at the ends and provided with an inlet branch at the top, and two side tubes 3 mm. bore leading into the ends. Copper amalgam was used for the liquid electrodes, and the tube was filled with the sol to be examined as follow: The tube was placed in the thermostat kept at 50-0" C., rubber tubes with clips were attached to the side tubes, and the amalgam was drawn up into both to a height of about 7 cm. above the level in the wide limbs. The sol-at a temperature of 70"-75O-was then filled in until it overflowed the inlet, a stopper inserted and tied in securely. The air was then admitted to the side branches and amalgamated copper wires immersed in the amalgam contained in them.The sol was allowed to assume the temperature of the thermostat, the amalgam adjusting itself to the contraction and maintaining perfect contact. After the measurements on the sol had been carried out, the whole thermostat was allowed to cool down to 30°, i.e. 3"-5" below the setting20 Amount of Dry Resistance Residue from of Column 100 Gm. of Gel. of Sol. ON CERTAIN PHYSICAL DIFFERENCES Resistance of Column of Gel. point, to ensure complete gelation, and was then slowly heated up to 50' again. The amalgam electrodes maintained perfect contact with the ex- panding gel. The apparatus used to determine the resistance of the sol and gel consisted of a metre bridge having a fairly uniform wire of resistance 5.79 x I O - ~ ohms/cm.A resistance box occupied one of the gaps, while the other contained the U-tube described above. The tube was placed in a thermostat provided with toluene regulator of the usual type; the temperature could be maintained within 0.1' C. Measurements were made with both direct current and alternating current. I n the first case the balance point was determined with a galvanometer having a sensitiveness of 5 - 2 x 104 div./volt, readings being possible to 1/10 division. In the case of alternating current the source of supply was a small coil giving a frequency of 384 per second, and the balance point was determined by means of a telephone. The current passing through the sol was about 5.0 x I O - ~ amp.with direct current and about z x I O - ~ amp. with alternating current. Tests were made for polarisation with direct current, but the effect was too small to determine. The procedure in any set of measurements was as follows : When the balance point on the bridge wire had attained a constant position it was assumed that the sol was at the temperature of the thermostat. Readings were then taken with both direct and alternating current over a period of ten minutes. The sol was then allowed to set to gel as described, and the latter re-heated to 50' and maintained at that temperature. When the balance point had again reached a constant position, readings were taken over the same interval as for the sol. Subsidiary experiments were made to determine certain possible sources of error; these are described below.ResuZts and Discussion.-I.n every case it was found that the conductivity of a gel containing copper sulphate was greater than that of the corre- sponding sol at the same temperature, viz. 50' C. The difference depends on the concentration of agar, and increases with increasing concentration, both for direct and for alternating current. The values obtained are set out below. The temperature at which they were determined was 50' C. in all instances. (a) With Direct Current. 2120 209.5 2021 I967 4;22 1960 I922 i 2*89 3 5 7 Nominal Conc. of Sol. Gel. 1-18 1-94 2-67 Per Cent. 3 5 7 Ohms. 215 3 I995 205 I Ohms. 2119 I95 7 2000 Difference. Per Cent. 1-58 1-91 2 '48BETWEEN SOLS AND GELS OF AGAR 21 No attempt was made to use sol or gel columns uf the same length between the electrodes in the three sets of determinations, and the values for different concentrations of agar are therefore not comparable.It will be noticed that for all concentrations the alternating current resistances of both sol and gel are uniformly about 1.5 per cent. lower than the corre- sponding direct current values. The differences in the conductivities of sols and gel at the same con- centration and temperature are not great, but much in excess of any possible experimental error. The magnitude of the latter depended on the accuracy with which the balance point on the bridge wire could be determined and the accuracy with which the temperature could be main- tained at 50'. The balance point could be determined easily to 0.5 mm.at the mid point with direct current and to 1.0 mm. with alternating current. This allows an accuracy of I in 1000 in the first case and of I in 500 in the second. As regards the possible error caused by imperfect temperature control, the temperature coefficient of conductivity was determined in the vicinity of 50' and was found to be 1.1 per cent. per degree C. As the tempera- ture was maintained constant within O-I', the possible error from this cause is of the order of I in 900. In all, therefore, the accuracy of the results is certainly I in 500, so that the error is much smaller than the observed differences in con- ductivity. Two possible factors remained to be investigated, which could account for, or contribute to, the difference in conductivity between sol and gel.With direct current there may have been polarisation at the electrodes and this may have been greater in the sol than in the gel. Failing this, the volume of the gel at soo may not have been the same as that of the sol at the same temperature, as had been tacitly assumed in the method of measurement. To test the first point, a current equal to that used in the actual measurements was passed through both sol and gel for two minutes and the balance points re-determined. The difference was not found to fall outside the limits of accuracy mentioned above. To determine whether there was any difference between the volumes of sol and gel at so', a U-tube dilatometer with one wide and one narrow limb was used, the ratio of the cross sections being IOO : I.Mercury was placed in the bend, and the wide limb was filled with about 10 C.C. of sol and sealed. Microscope readings were taken of the level of the mercury in the narrow limb with both sol and gel at soo. Any difference between the two volumes was thus greatly magnified, but it was found to be less than 0-002 per cent. The difference in the resistance of sol and gel is therefore not due to any difference in length of the columns between the electrodes. While comparison at one temperature is sufficient to establish a definite difference between agar sol and gel containing electrolyte, investigation over an extensive interval of temperature appears desirable and will be carried out at the first opportunity. Meanwhile the only-highly specu- lative-explanation of the difference which suggests itself is the following : if gelation is the segregation of a phase much richer, and an aqueous phase much poorer in agar than the sol, the aqueous phase may carry most of the current and may, notwithstanding the obstruction by the gel phase, owing to its low viscosity offer less resistance than the viscous sol.This22 DIFFERENCES BETWEEN SOLS AND GELS OF AGAR explanation involves the further assumption that the electrolyte remains wholly or largely in the aqueous phase, a point on which there is obviously no evidence. Diffusion experiments in sols and gels at the same tempera- ture would provide useful evidence, but although a great number of different arrangements have been tried by one of the authors, the experimental difficulties seem to be almost insuperable.As regards the result that the resistances of both sols and gels are uniformly lower with alternating than with direct current, two-thirds of this difference was observed in an aqueous solution of copper sulphate of the same concentration, in the absence of agar. Such a solution was placed in the conductivity vessel and treated in exactly the same way as the sols and gels. The direct current resistance was found to be about I per cent. higher than the alternating current resistance. The difference was not due to polarisation, as the application of direct current for 1.5 minutes caused the resistance to change by only 0.1 per cent. SUMMARY. Agar sols and gels containing 3 per cent. and more of agar show marked optical differences, inasmuch as the sols are clear in transmitted and reflected light, while the gels, though clear in transmitted light, show marked opalescence in reflected light. Owing to the lateral scattering of light, the gels also appear darker in transmitted light than the correspond- ing sols. The opalescence does not decrease when the gels are kept for several days at a temperature of 62' C., i.e. about midway between the setting and melting point. The conductivity of agar gels containing electrolyte is greater, for both direct and alternating current, than that of the corresponding sols, the difference increasing with increasing concentration of agar. The conductivity of agar sols and gels containing electrolyte is greater for alternating current than for direct current, the difference being slightly greater than that between the alternating and direct current conductivities of aqueous electrolyte solution of the same concentration without agar. Th Sir John Cass Technical Institute, London, E.C. 3.

ISSN:0014-7672    

DOI:10.1039/TF9242000018

出版商:RSC    

年代:1924

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. 22 DIFFERENCES BETWEEN SOLS AND GELS OF AGAR DISCUSSION. Professor J. W. McBain. (Communicated). A GENERAL CONCEPTION OF NEUTRAL COLLOIDS, AND ITS BEARING UPON THE STRUCTURE OF GELS AND TRUE JELLIES.The interesting observations communicated by Messrs. Hatschek and Humphry show that there is a distinct although slight difference between the conductivities exhibited by copper sulphate in agar sol and gel. Again, the difference in appearance between sol and gel of agar is real and un- doubted. May I suggest, however, that the resemblance between sol andgel, apart from such mechanical properties as rigidity and elasticity is far more striking than their differences ? The discussion of solutions of agar or gelatin containing an extraneous electrolyte is necessarily more complicated than that of soap since in soap sols and gels it is the constituents of the soap that themselves determine such properties as conductivity and osmotic activity and reveal that equili- brium is essentially unchanged when they form a jelly.In view of this I would deprecate the " highly speculative explanation " put forward for agar sol and gel since it tends to emphasise their difference and because it does not well accord with our experience of soap solutions. It is assumed that the conductivity would be greatly dependent upon the viscosity but in soap solution it is found that the conductivity is not very much affected by change in viscosity of many hundred fold. All that it is necessary to assume is that the particles existing in the sol, in arranging themselves to build up the jelly structure, do not thereby appreciably influence the conductivity. Nevertheless the real though slight differences between, the particles in sol and gel accord well with the general conception which we have found a useful guide in our work during the past few years.This is to the effect that a linking together of colloidal particles to form larger structures, is caused by bonds of union which are at least as local and specific as the processes operative in adsorption or residual affinity. These bonds are loosed by the substitution in them of various suitable chemicals. Such action would be postulated in dissolving colloidal materials such as nitro- cellulose or rubber. Here this generalised form of solvation becomes the essential factor and electrical charges (so often invoked through preoccupa- tion with suspensoids) are of minor significance. The bonds between the particles are restored if the suitable localities of those particles are deprived of their chemical complements (not necessarily molecules of the solvent) whether by change of temperature, addition of diluents, lowering of vapour pressure or direct chemical action.According to this working hypothesis the one great operative force to be taken into account is solvation and specific combination, whether physical or chemical, with the molecules of colloid. A colloid of this type becomes soluble because its surface is given a sufficient degree of similarity to the solvent medium ; it is common knowledge that compounds of similar char- acter, such as hydrocarbons, are mutually soluble. The linking up of particles to form a gel structure (whether filamentous, brush-heap, etc.) would lead us to presuppose a splitting off of some sub- stance from the points of union and in the present cases this would consist of localised dehydration.In the absence of any measurements of the re- spective compositions or amounts of the various crystalloidal and colloidal constituents of the agar sols and gels, it is not worth while entering into a detailed discussion, although it is seen at once that the application of our working hypothesis would explain the slight increase in conductivity observed when the particles of agar unite to form the gel. The hypothesis emphasises the importance of aggregates as colloidal units and finds further application in the behaviour of clouds and smokes. I t underlies the convenient classification of colloids into three groups pro- posed by the writer in Nature (March loth, 1921, 107, .p.46) ; namely neutral colloids, suspensoids, colloidal electrolytes ; whilst it recognises that these are but extreme types with a continuous series of intermediate gradua- tions (for diagram seeJourn. Suc. Chem. lnd., 1923, 42, 616).24 DIFFERENCES BETWEEN SOLS AND GELS OF AGAR Szmmary. A general conception is advanced to explain the stability of large groups of colloids and their behaviour in solution, coagulation and gelatinisation. Department of Physical Chemistry, University of Bristod. Mr. J. H. Shaxby (commzinicated) : I n the course of experiments made some time ago on electrode polarisation I had occasion to measure the conductivities of certain electrolytes, chiefly ferrous sulphate and ferric chloride solutions, both by direct and alternating currents.I found the same difference as do the authors : the direct current measurements of re- sistance were nearly I per cent. greater than the alternating. This difference was not due to polarisation. The resistances were of the order of 500 ohms. I have noticed the same thing in measuring the resistance of blood serum; here the difference was somewhat larger but I cannot state that it may not have been in part due to polarisation, though the conditions were such as should have made any polarisation very small. I n this case the resistances were of the order of zo,ooo ohms. Mr. A. Highfield: The authors state that “meanwhile the only- highly speculative-explanation of the difference which suggests itself is the following : if gelation is the segregation of a phase much richer and an acqueous phase much poorer in agar than the sol, etc.” This explanation implies that the sol to gel transition in this system is due to the separation of two colloidal systems, one richer in agar than the other. The phenomenon of a colloidal sol separating into two colloidal systems in equilibrium with each other is quite common in the case of sols in mixed solvents. I t is submitted that a study of the conditions associated with such a separation will throw light on the agar sol to gel transition.I n the case of cellulose acetate in mixed solvents it would appear that thermally reversible sol to gel transitions are of the nature of a separation of a colloidal sol into two colloidal systems.On this explanation the maximum gelation temperature is a critical temperature similar to that of partially miscible liquids. Weissner and Bloxham 1 working with arsenate jellies have shown that the conditions for gel formation in these systems are the precipitation of a hydrous substance in an exceedingly fine form, which substance absorbs the solvent water strongly. Very slow precipitation favours gel formation whilst rapid precipitation results in gelatinous precipitates. Ether-alcohol solutions of nitrocellulose further illustrate the conditions required for gel formation. Five per cent. solutions of nitrocellulose in ether-alcohol mixtures are usually sols. Hut if much ether be present, say 92 per cent., such systems are typical elastic gels. If sufficient ether is added to bring the ether content to 94-96 per cent.with agitation and the mixture finally allowed to stand it separates into two colloidal systems in equilibrium, one rigid and the other fluid. The rigid “ phase ” is richer in nitrocellulose and poorer in ether than the fluid “ phase.” If great ex- cess of ether be present the more rigid “ phase ” is so rich in nitrocellulose as to be sensibly precipitated gelatinous nitrocellulose, Finally, whilst such mixtures containing 9 2 per cent. of ether dissolve nitrocellulose, yourn. of PJiyYs. Chcm., XXVIII., 1924, 26.DISCUSSION Benayl Alcohol. 25 Nitrobenzene. mixtures containing 94-96 per cent. of ether merely cause it to swell. Ether itself is without action.Thus dilute ether-alcohol solutions of nitrocellulose are gels if the solvent power of the solvent is poor and if the solvent is closely similar in composition to liquid mixtures which do not dissolve the nitrocellulose but to merely cause it to swell. Extending this line of argument to thermally reversible transitions-on cooling the sol from a temperature above to one below the maximum gelation temperature the sol would be expected to separate into two colloidal systems, one richer in the solute than the other but both containing solvent and solute. If the amount of cooling is slow enough to ensure a fine grained structure gels should result, being clear or cloudy depending on the size of the structure and the relative refractive indices of the two colloid systems.But if the amount of cooling is so great that the systems are very markedly different coarse structures such as curds should be pro- duced. We should further be able to raise or lower the temperature of maximum gela- tion in the same manner that we can alter the critical temperature of partially miscible liquids such as alcohol and kerosene by addition of a third ingredient. In the alcohol-kerosene system water raises the critical temperature because it is soluble i n alcohol and very insoluble in kerosene. Similarly a solvent which is miscible with both of these liquids lowers their critical temperature. All of these expectations are experimentally realised in the case of cellulose acetate and benzyl alcohol gels. The maximum gelation tempera- ture of 10 per cent.cellulose acetate sols in benzyl alcohol is about 25" C. Ethyl alcohol is soluble in benzyl alcohol but is not a solvent for cellulose acetate and should therefore raise the maximum gelation temperature. Nitrobenzene should have the opposite effect because it is a solvent for cellulose acetate and dissolves in benzyl alcohol. The table below shows the composition of several 10 per cent. sols of cellulose acetate in these solvent mixtures which were made to test this point. I n the limit a gelatinous precipitate should be obtained. 93'7 88.3 82'0 76-9 _ ~ _ _. ___ I Solvent . 1 Benzyl Alcohol. I Ethyl Alcohol. Sol No. 6.3 11.7 I 8.0 23.1 I 100'0 95'7 91.8 87'7 83'6 78.8 74'4 69-8 0'0 4'3 8.2 12.3 16-4 25.6 30.2 21'2 - Sol No. - - I - 2 - 3 - 4 I The sols were heated to 60" C., then placed in constant temperature baths at various temperatures and the rate of gelation measured in the manner chosen by E.Mardlesl by plotting a viscosity-time diagram. Rapid increase in viscosity indicated gelation. The curves showing viscosity against time for all the sols at six chosen temperatures are given in Fig. I. 1 E. Mardles. Tvaas. Faraday SOC., XVII I., 1923, 327-36 j. VOL. XX-TZ26 DIFFERENCES BETWEEN SOLS AND GELS OF AGAR Thus at 24' C. the sols containing nitrobenzene do not set. in benzyl alcohol sets slowly. rapidly, the rapidity of gelation increasing with the alcohol content. That made The sols containing alcohol set more At w = I!! TIME'-----+ FIG. 2. 70° C. only the sols containing 18.0 and 23.1 per cent.of nitrobenzene do not gelate whilst at 35' C., only those containing 20 per cent. and more of alcohol gelate. From a series of such curves the maximum gelation temperature ofDISCUSSION 2 7 each sol can be obtained and Fig. 2 shows the relation between that tem- perature and the solvent composition. Further all the solutions were heated to 60" C. and cooled rapidly by placing in a constant temperature bath at 15' C. All gelated except the sols containing more than 12 per cent. of nitrobenzene. The gel containing 6.3 per cent. of nitrobenzene was slightly cloudy, that in benzyl alcohol a little more so and then the cloudiness increased with the ethyl alcohol content. The gel containing 30 per cent. of alcohol presented all the ex- ternal appearances of a typical curd.With more alcohol than this (not given in the table) marked syneresis occurred even to the extent of coagula- tion of a gelatinous precipitate. The very close similarity between these results and those of Weissner and Bloxham with arsenate jellies is very significant. I t is therefore sub- mitted that the thermally reversible sol to gel transition in such cellulose acetate systems is due to the segregation from the sol of two colloidal systems in equilibrium (one probably rigid)-the phenomenon of maximum gelation temperature being in all respects similar to the critical tempera- ture of two partially miscible liquids. I t is of course in no sense claimed that gel structure is explained on this theory. At the maximum gelation temperature the colloidal systems which separate may be so finely divided that the system may be as homo- geneous as the sol in which case it must be regarded as merely orienting itself prior to segregation.But below that temperature the separation of the two systems is niuch more obvious. Professor Alfred W. Porter asked what is the effect of adding agar to the solution. I f the copper sulphate were in water alone, what would the conductivity be? Before any conclusion could be formed as to the suggestion with regard to two phases, one specially rich in one of the constituents and the other specially rich in the other constituent, we really want to know what effect the agar itself has. H e did not think there need be any difference, or any great difference, between the gel stage and the sol stage if we were to judge from the scattering of the light.The scatter- ing was proportional to the square of the relative index, so that a very little change rapidly increased it. The amount of light scattered from the gel is actually exceedingly small although it is a conspicuous effect to look at. The mere fact that the gel was rigid and the sol was not was a better in- dication that some considerable change had occurred. With regard to the electrical effect mentioned it was just possible that in the narrow interstitial spaces in the liquid phase, the ionisation is different from what it would be in the body of the solution, and if this is so it might account for the small difference observed. With regard to the difference to expect between steady current and alternating current, he was not quite sure.The mere existence of the capacity at the electrodes introduced some complications in dealing with alternating current and until he knew exactly what that capacity was, he would not like to predict which way it would go. He took it that the experiment showed it went towards diminishing the effect. Mr. F. S . Spiers : Would not varying the frequency tell you ? Mr. Hatschek : We have only tried one frequency. Dr. J. N. Pring: If the difference in conductivity with direct and alternating current in the case of copper sulphate and other salts mentioned was a real effect, it seemed a point of fundamental importance. I t may be taken as well established that in the case of most salts, no appreciable difference has so far been found to arise from the nature of the current, and this assumption forms the basis of most conductivity data.The effect28 DIFFERENCES BETWEEN SOLS AND GELS OF AGAR of frequency on conductivity has been investigated more particularly by E. D. Eastman,l who found, in the case of potassium chloride and sulphuric acid, that the conductivity was higher by about 0 - 0 2 per cent. in the case of alternating current of a frequency of 1000 than with direct current. The difference is considered to be a real one and to be due to oscillatory rotation of polar groups of molecules, but the magnitude of the difference is of a much smaller than that indicated by Dr. Hatschek and Mr. Humphry. Dr. J. Reynolds remarked that the behaviour of the gel described by the authors, recalled that of reversible emulsions, which may perhaps be regarded as extreme cases of gels.Such an emulsion, in which the aqueous phase is the continuous one, might be a fair conductor of elec- tricity, but if warmed until inversion occurs (generally accompanied by increase of viscosity) is found, on cooling, to be highly resistant, like the oil which is now the continuous phase. Dr. J. S. Sand (communicated): I have been much interested in the result that the resistance of a copper sulphate solution, both in the presence and in the absence of agar, was found greater with continuous than with alternating current. So far as I am aware, no definite results regarding such differences have been hitherto recorded, most experimenters having come to the conclusion that the resistance to the two forms of current was the same.As I have pointed out on another occasionY2 the theories of strong electrolytes in which the latter are assumed completely ionised at all concentrations and in which the variations of molecular conductivity with dilution are ascribed to the electric fields created by the ions, all lead to the conclusion that conductivities should be greater for alternating current than for direct, and also that they should be slightly greater for very high currents than for low. I have hitherto considered the fact that no effects of the kind have been observed, to be the principal argument against theories of the kind referred to. I t seems to me that the matter urgently requires further investigation. Mr.E. Hatschek, replying to the discussion, said that Professor Porter had probably raised the most important point, i.e. why the gel became rigid. Professor McBain had said on several occasions that, apart from the elasticio and rigidity, there was not much difference between a sol and a gel. I t seemed, however, to be difficult to disregard this change in elasticity and rigidity, when one saw an agar sol, which above 35" was a liquid, normal apart from the well-known anomalies of viscosity, turn into a system which, under small stresses applied for a short time, behaved like a perfectly elastic solid, with a quite measurable modulus of rigidity and tensile strength. To insist on the identity in conductivity and refractive index, and to disregard the difference in elastic properties some- what resembled the attitude which the ostrich was said-as we were now told, unjustly-to assume in the face of trouble. As regarded Mr.Highfield's remarks, the data quoted by him gave support to the view that gelation involved a change in the agar concentra- tion in the two phases-a view which differed from that of Professor McBain, who postulated merely a linking up of particles pre-existing in the sol, with dehydration at the points of linking as a possible secondary change. The parallel between this separation and the segregation of im- perfectly miscible liquids had often been drawn, and might be useful as an y o u ~ n . Anzer. CILenz. SOC., 1920, 42, 1648. Phil. Mag., 1923, Vol. XLV., p. 284.DISCUSSION 29 illustration : the most striking feature of gelation, however, the formation of an elastic solid, could not be imitated by a liquid-liquid model. He quite agreed with Professor Porter that a very small change in the refractive index of one phase might account for even the striking turbidity of the 5 per cent. agar gel. On the other hand, if the optical differentiation during gelation was, as he firmly believed, due to changes in hydration, a considerable shifting of water from one phase to the other might be required to produce even a small change in refractive index. H e had no explanation of the difference in conductivity, and was pre- pared to accept Professor McBain’s suggestions, as far as they went and as far as he understood them. He had received other suggestions from friends who had been kind enough to take an interest in their results : thus Professor v. Weimarn had taken the trouble to write that by the aggrega- tion or growth of particles during gelation, and the consequent reduction in surface, adsorbed electrolyte might be liberated, which would account for the higher conductivity of the gel. Mr. Humphry and he had felt that, as no such measurements had apparently been carried out before, they would serve a useful purpose, and would supplement the results obtained by Professor McBain and Miss Laing with soap. All these results would eventually have to be taken into account in any theory of gelation, but he felt confident that any such theory would have to explain the elastic properties of gels if it was to satisfy any large number of observers.

ISSN:0014-7672    

DOI:10.1039/TF9242000022

出版商:RSC    

年代:1924

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. THE INFLUENCE OF ANIONS IN THE COAGULATION OF A NEGATIVE COLLOIDAL SOL. BY D. C. HENRY AND V. A. MORRIS. ( A Paper read Before THE FARADAY SOCIETY, Monday, February 18th, I 924, SIR ROBERT ROBERTSON, K.B.E., F.R.S., PRESIDENT, in the Chair.) Received November 2 7 th, I 9 2 3. ABSTRACT. The coagulating power of an electrolyte for a lyophobe sol is largely determined by the nature of the ion of opposite sign to the colloidal particle, but is also influenced by the ion of the same sign, which exerts a stabilising action.Experiments have been carried out on the coagulating powers for a (negative) gold sol of a series of salts of the same cation (sodium), with the object of determining the relative stabilising powers of the different anions. For each salt the curve was traced connecting electrolyte con- centration with the time required to reach a definite arbitrary stage of coagulation, estimated by a colorimetric method. If the logarithms of the electrolyte concentrations and the corresponding coagulation times are plotted, the curves obtained are either linear or of small curvature.The results indicate the following sequence of stabilising power of various anions when associated with sodium ion in the coagulation of a gold sol : oxalate > HPO,” > Cog”,> OH’, citrate > HCO,’ > Br’, 1’, acetate, valerate > butyrate, CNS’ > SO,” > C1 , benzoate. I. Introductory.-The coagulation of a lyophobe sol by the addition of electrolytes is commonly attributed to the partial or complete neutralisation of the electric charge of the colloid particle by the adsorption of ions bearing a charge of opposite sign. Little attention has hitherto been paid to the influence of the ion which has a charge of the same sign as that of the colloid although, as several writers1 hsve pointed out, its effect must be considerable, since the coagulating powers of various salts, all containing the same ‘‘ coagulating ion,” differ considerably among themselves.2 The experiments reported below were undertaken in order to obtain semi-quantitative indications of the stabilising effect of various anions when associated with one and the same cation in the coagulation of a negative gold sol.Sodium was selected for the invariable cation on account of the solubility of its salts. In measuring the coagulative powers of a series of salts no attempt was made to determine a “threshold value ” of the concentration, below which the sol remained stable, and above which slow coagulation ensued. In- stead of this, measurements were made of the time required for the sol to reach a definite stage of coagulation in the presence of various concentra- tions of electrolyte.The coagulative powers of the various electrolytes are deduced from a comparison of the respective time-concentration curves thus obtained. ’Ostwald, Koll. Zeitschr., 26, 28, 69, 1920; Bancroft, Second Report on Colloid Chemistry, pp. 9, 11 ; Weiser and Nicholas, yourn. Phys. Chem., 25, 742, 1921 ; Bach, Joum. de Chem. Phys., 24, 701, 1920. 2 See, for example, the table of coagulation values collected in Burton’s Physical Properties of Colloidal Solutions, p. 158. 30ANIONS AND A NEGATIVE COLLOIDAL SOL 9-80 9-21 10.40 9'57 10.73 9'77 11-47 10.32 11-87 10.56 12.80 11-26 11.11 10'11 31 16.2 8.0 6'0 4'1 3'1 2'2 2'0 2. ExperimentaL-The gold sols used in the experiments recorded were made by Zsigmondy's " nucleus method," and were dialysed in collodion thimbles against conductivity water till the conductivity of the sol fell below I O - ~ reciprocal ohms.A colorimetric method of following the coagulation was employed. Definite volumes of gold sol and of electrolyte solution of suitable con- centration were simultaneously poured from separate test tubes into one cup of a Dubosc colnrimeter in such a manner as to ensure complete and rapid mixing. The depth of the layer to be examined was adjusted to a fixed value, and the time noted at which the sol matched a standard tint placed in the other limb of the colorimeter. The standard tints were pre- pared of stained gelatin cemented in glass, and were protected from light when not in use. No great precision was obtainable in the evaluation of the coagulation time ; the average deviation from the mean of duplicate determinations was about 8 to 10 per cent.All solutions were made up with water of conductivity about 10 - 6 re- ciprocal ohms, prepared in a still with silver condenser ; they were stored in Jena glass vessels cleaned with caustic soda and Beckmann's mixture. 3. Experimentad ResuZts.-In the table of results given below, c1 de- notes the final concentration of the electrolyte, after mixture with the sol, in millimols per liter, c2 denotes the corresponding concentration of sodium ions in milligram-ions per liter. In view of the low precision in the values of the coagulation time, it has been considered adequate to calculate cz from c1 by interpolation from the following typical '' degrees of dissocia- tion " : for uni-univalent salts, at 0.01 N, a = 0.94 ; at 0.05 N, a = 0.87, for uni-bivalent salts ,, ,, a = 0.87 ; ,, ,, a = 0-78, for uni-trivalent salts, ,, ,, a = 0.82 ; ,, ,, a = 0.70.t denotes the time in minutes required to reach the standard stage of coagulation, and is the mean of zz determinations. 85.0 37'5 13.1 5.1 1'5 2'2 1'0 TABLE I. 10 C.C. of sol mixed with 5 C.C. of electrolyte solution. Series 1.-Sol B, Standard Tint B. -~ __ c1. 1 c.3 j t . I I t . 2 2 2 2 2 2 2 ~ _ _ _ _ ( I ) Sodium Chloride. 34'70 36-23 36'70 37-00 37-88 55'52 57'97 58-72 59-20 60.61 21.52 22'28 22'88 25-04 27-07 27'97 29-28 19-52 20'16 20'66 22-53 24-28 25.04 26-12 5'55 6'66 6'93 7'23 7'56 8.3 3 (2) Sodium Sulphate. 9'99 I 1'85 12-33 12'72 13-31 14.66 29-0 6.7 3'8 10'0 2'1 0.8 (4) Sodium Oxalate.13.7 7'5 2'9 0'4 I 'I 2 3 3 3 3 2 2 2 2 2 232 THE INFLUENCE OF ANIONS IN THE COAGULATION Series 11.-Sol D, standard tint D. 5 C.C. of sol mixed with 2 C.C. of electrolyte solution. n. 2 2 3 3 3 3 3 3 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 2 2 2 3 3 2 j) Sodium Chloride. 6) Sodium Bromide. 40.81 41-71 42-85 43'95 45-11 46-34 47'62 49'27 35'87 37'58 38'50 39'47 40.50 41-53 42'92 36-62 26'0 18.0 9'9 5'5 3 '5 2'5 1 '5 0.8 13-18 13-85 14-20 14-58 15-40 16-30 17-36 17-93 30.0 20.5 13'7 9'9 6.0 4'1 2'1 1'2 14-29 15'04 15'44 16-81 19.05 19-70 15-87 17-85 37'53 39-09 40.80 42'65 44-68 46'91 49'38 55.20 (7) Sodium Iodide. (8) Sodium Thiocyanate. 29'31 30'44 31-66 32'9l 34'42 3 5'97 37'69 39'58 26-18 27-14 28-18 29-26 30'5 7 33'29 31-83 34'83 33-06 34'40 35-86 37'41 39-10 40'95 43*0= 47'75 33'5 24 '5 15'5 9'5 4'7 2'5 0.7 2'1 31'0 16.0 9'0 4'7 3'1 2'2 1'5 0 -6 (9) Sodium Hydroxide.10) Sodium Benzoate. 60'00 61-92 64-00 66-20 68'56 71-12 80.00 73'84 75-80 51'90 53'44 55-11 56'87 58-76 60.82 62-99 64'51 67-76 24.0 16.5 12.4 8.8 7'0 4'5 2'5 0'4 1'0 13'79 14'57 15'00 15-45 15'94 16-30 I 7 -00 17-59 18'89 12-71 13.42 13-80 14-20 14-63 14'95 15-56 16-08 17.21 23.0 11.9 9'0 7'0 4 '5 3'9 3'0 2'0 1'0 (I I) Sodium Bicarbonate. (12) Sodium Carbonate. 38-54 38.93 39'37 40'22 42-05 44'04 46'25 60.90 61-52 62-13 63.40 66.1 I 63-97 72-15 30'5 16.1 5 -6 10'0 3'0 0.9 2'1 50'55 9-42 52-24 53'92 55'72 59'69 44'03 44'69 45'29 46-70 48-14 ' 51'46 32'5 14.0 7'9 3'8 2.4 0'6 (13) Di-sodium Hydrogen Phosphate.(14) Sodium Citrate. 26-0 20'0 12'0 8.0 3'7 1 '9 0'5 1'1 69-80 70.83 72-00 73-20 74-28 76'85 79'59 20.3 9'1 6 '5 3'0 2'4 0.5 1'0 52-18 52-83 53'52 55-01 56-51 58.18 59'87 61-69 44'63 45'35 46'16 46-97 47.80 49-58 51-48 -- 22-62 22-96 23-29 24-00 24'75 25'55 26-40 27-31OF A NEGATIVE COLLOIDAL SOL 33 15-89 14'59 36.7 17-21 15-76 8.0 18.77 17'12 3'9 20.65 18.77 2'0 22'95 20'75 1'0 16.39 15-03 17'0 Series 111.-Sol E, standard tint D. 5 C.C. of s.31 mixed with 2 C.C. of electrolyte solution. 2 2 2 2 2 2 18 16 14 Sol E / I. (17) Sodium Valerate. 1 19-81 20'44 2 I -96 22'75 23-71 24'70 26-95 IS-03 18.60 19.90 20.57 21-41 22-26 24.15 25-47 30.0 16.0 7'5 6.0 4'1 3'0 1 '4 0'9 was a portion of sol D which had remained standing for some weeks after its use in Series 11.Its properties had changed in-the mean- time, as is shown by a comparison of experiments ( 5 ) and ( I s). 4. DiscussLm-The time-concentration curves are of the usual type (Fig. I), showing at low concentrations a rapid increase of coagulation time with increase in electrolyte content, and at higher concentrations a tendency for the coagulation time to approach a lower limit. This limit, which corresponds to the region of "rapid coagulation," was not nearly reached in any of the experiments carried out. For purposes of comparison, it is convenient to plot log c, against log # (Fig. z ) , since not only is the whole diagram thus reduced to manageable size, but also the resulting graphs are found to be lines of small curvature. I n fact for more than half the electrolytes employed the logarithmic curves are linear within the error of experiment, corresponding to the relation C, = ktp, where k and p are constants specific to the electrolyte, p being always less than unity, This relation cannot have any extended validity, since it allows neither for a '' threshold value," nor for a region of " rapid coagula- tion," where the time is independent of the electrolyte concentration within34 THE INFLUENCE OF ANIONS I N THE COAGULATION wide limits.’ With the exception of that for sodium hydroxide, those curves which are not linear are convex to the log t axis, a behaviour which 1 ‘9 1.8 = ‘3 I ‘2 I ’I \ NaSQ I -6 0’0 1‘0 log t 2’0 FIG.2.-Collected logarithmic curves, all reduced to standard of Series 11.Series I., 1.1; Series lI., 0, 0 ; Series III., A. is no doubt characteristic of the complete log c,-log t relation (6 Paine and Evans,2 who have measured the rate of coagulation of a gold sol over Zsigmondy, Zeitschv. F. Elektrochem., 23, 148,1917; ‘ I Kolloidchemie” (xgzo), p. 66. Paine and Evans, Trans. Faraday SOC., 19, 649, Feb. 1924.OF A NEGATIVE COLLOIDAL SOL 3 s wide ranges). The sodium hydroxide curve shows a decided bend in the opposite direction at higher concentrations, indicating that this electrolyte in sufficient quantity tends to act as a stabilising agent rather than as a coagulant. This is not an entirely unexpected conclusion in view of the exceptional adsorbability of the hydroxyl ion. The results of Series I., 11. and 111. are not directly comparable, being made with different sols; the experiments performed in each series with sodium chloride provide, however, a rough basis for intercomparison, if we make the plausible assumption that, for a given coagulation time, the ratio of the corresponding concentrations in different series will be the same for all electrolytes.This assumption is probably justifiable for electrolytes of the same type,l but is more doubtful when applied to electrolytes of different types.2 The transformed results for sodium sulphate and oxalate should therefore be accepted with reserve, and are bracketed as doubtful in the final table of this paper. In Fig. 2, all the curves have been adjusted in the above manner to the standard of Series 11. It is interesting that, whereas the correcting ratio, deduced from the sodium chloride curves, for the comparison of Series I.and 11. varies with the coagulation time, that for Series 11. and 111. is independent of the latter, a circumstance which may very likely be connected with the fact that these two series differ only in the initial states of the sols, E being probably a partially coagulated specimen of D. From the logarithmic curves of Fig. z it is evident that there is no invariable order of coagulating power among the salts used, since some of the curves intersect. By grouping together substances whose curves are close together we obtain the following sequence of anions in descending order of stabilising power. The numerical factors given are the rounded- off values of the concentration of sodium ions required to bring about coagulation (on the standard of Series 11.) in ten minutes in the presence of the equivalent quantity of the respective anions, and may be taken as approximate measures of the stabilising powers, per equivalent, of the latter.The sequence of anions obtained above agrees neither with the orthodox Hofmeister adsorption series, nor with the order of coagulative power of anions for positive sols, as determined by Freundlich and TABLE 11. Ion. [Oxalate . . Hydrogen phosphate Carbonate . . Hydroxyl . . Citrate . . . Bicarbonate . . Bromide . . Iodide . . . Acetate . . . Valerate . . Butyrate . . Thiocyanate . . [Sulphate . . Chloride . . Benzoate . . . . . . . . . * . . . . . . . . . . . . . . . . . . . . . . 851 70 63 55 45 35 28 181 14 1 See, e.g., Bach, loc. cit. 2 See, for example, Burton and Bishop, yourn. of Phys. Chem., 24, 701, 1920.36 ANIONS AND A NEGATIVE COLLOIDAL SOL others. on the coagulation of arsenious sulphide, Bancroft has deduced that the stabilising power of the anions is as follows : citrate > acetate > formate > sulphate > nitrate = chloride. This sequence is in complete agreement with that of Table II., so far as the two overlap. The various sequences of ions deduced by different workers for adsorp- tive and coagulative processes indicates, however, that ionic adsorption is highly specific to the adsorbent, and that no invariable “Hofmeister series ’’ is to be expected. The approximate rule that multivalent ions have a greater influence on coagulation than univalent is roughly borne out by our measurements. This work is being continued, both with a view to obtaining a higher degree of accuracy, and with the object of throwing light on the process of ‘‘ slow coagulation ”. From the measurements, however, of Freundlich and Schucht The authors wish to express their thanks to Dr. Powell White, Director of the Helen Swindells Research Laboratory, for the loan of the colorimeter used in this research. 1 Freundlich and Schucht, Zeitschr. f. Phys. Chew., 80, 564, 1912. Bancroft, Second Report (iit Colloid Chemistry, p. 11. Thomas Graham CoZZoid Research Laboratory, Victoria University of Manchesfer.

ISSN:0014-7672    

DOI:10.1039/TF9242000030

出版商:RSC    

年代:1924

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. 36 ANIONS AND A NEGATIVE COLLOIDAL SOL DISCUSS.lON. Mr. E. Hatschek said the suggestion that the effect of the anions in the coagulation of negative sols had to be taken into account had been made several times in recent years, more particularly two or three years ago by Wo. Ostwald in a comprehensive paper. On the other hand, Michaelis and collaborators threw doubt on the part played by the anion, and suggested that the combined effect the cation and the hydrogen ion was the essential factor. He was surprised to see from the authors’ work that the stabilising effect of the citrate ion was so low. Mr.Henry : So were we. Mr. Hatschek continuing said it would be interesting to try whether it was possible to get a red gold sol by reduction with oxalate ; it was of course quite easy to do so with citrate. Dr. H. Borns asked if he understood from the authors that colour was a criterion of the state of coagulation. Mr. Henry: Yes. Dr. Borns said he thought Zsigmondy had shown that there was no simple connection between the colour of a sol and the size of the particles. Mr. Henry said that Zsigmondy had shown that, for a given sol, a given colour corresponded to a definite stage of coagulation, as determined ultramicroscopically. Mr. A. Highfield asked if it were not a fact that the hydiogen ion concentration had a lot to do with the colour. Could that be put down entirely to size? Mr. Hatschek said he would not like to say. The question was difficult, since one could obtain red sols both in acid medium, e.g. by re- duction with alcohol or tannin, and in alkaline medium, e.g. by reduction with formaldehyde or dextrin. The colour probably depended on the com- position of the ‘L gold.”

ISSN:0014-7672    

DOI:10.1039/TF9242000036

出版商:RSC    

年代:1924

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. THE DIFFUSION POTENTIALS AND IONIC MOBILITIES OF BENZOATES AND SALICYLATES, AND THEIR MODIFICA- TION BY A MEMBRANE OF PARCHMENT PAPER.BY EDMUND BRYDGES RUDHALL PRIDEAUX AND WILLIAM ERNEST CROOKS. ( A Paper read before THE FARADAY SOCIETY, Monday, February rgth, 1924. SIR ROBERT ROBERTSON, K.B.E., F.R.S., PRESIDENT, in the Chair.) ReceivedJanuary 27t.4, I 924. It is well known that diffusion potentials are modified, and generally increased, by the interposition of animal, vegetable, and artificial membranes. This increase is naturally attributed to a decrease in the transport number of the slower ion, with a consequent increase in the value of I - zn, in the usual equation, eg., when the anion is the slower. On this view the slower ion is proportionately more impeded, yet neither is completely unable to pass, as in the case of the true semipermeable membranes which have received so much attention.In the cases which we consider then, the potentials are not permanent since the electrical double layer slowly moves towards the side of lower concentration. But these membrane potentials, unlike diffusion potentials, can be restored to their original values by stirring on each side of the solutions, if the volumes of these are large relatively to the area of the membrane and the rate of diffusion is slow. Some time ago it occurred to one of us that these potentials were best treated as modified diffusion potentials and quantitative measurements on sodium benzoate gave results in accordance with the theory.’ The present work extends the measurements to potassium benzoate and salicylate and indicates that the parchment has a specific effect on the transport number.The theoretical justification for our method of treatment of these mem- brane potentials may be found in the following possible mechanisms. (I) The concentration gradient is supposed to lie completely within the membrane. This condition is fulfilled when the diffusion in the mem- brane is slow and the solutions on each side are stirred. If the membrane is completely impermeable to one ion there cannot be a diffusing zone in the membrane but there will be electrical double layers at the two solution- membrane interfaces with an attempt to set up Donnan membrane equilibria. I t was found that sodium benzoate solutions separated by a membrane of copper ferrocyanide gave inconstant potentials, in some cases nearly equal to the theoretical values when n, is 0.In order that the potentials may be constant from the first it s,eems necessary that the anion should have a mobility, even if only a low one, in the membrane. Trans. Far. SOC., X., 160, August, 1914. 3738 DIFFUSION POTENTIALS AND IONIC MOBILITIES OF C = 0.03697 0'020 I I ( 2 ) Alternatively, the potential can be considered as being due to two electrical double layers, one at each bounding surface between solutions and membrane. The theory of Riesenfeld and Reinhold is app1icable.l These authors consider the case of a salt present in two concentrations, and separated by a diaphragm of phenol saturated with water and the salt. The phenol diaphragm is supposed to consist of two layers having concen- trations in partition equilibrium with the two salt concentrations C, and C, respectively.I t was shown that the total potential difference between anion reversible electrodes (e.g., Hg, Hg,Cl,) would be equal to 0'01077 0~00562 0~00293 zn,RT log CJC,. Also when the two phenolic layers are mixed and are therefore no longer in partition equilibrium with C, and C, it was shown that, if the concen- tration in this phenolic diaphragm is low compared with C, and C,, the potential difference will be given by the same expression. T h e MobiZifies of the Benzoic and SuZiyZic Ions. I n calculating these from the conductivity results (at 25') available in the literature, it became evident that the agreement between them was not sufficiently good to enable the values of the mobilities to be defined within I or 2 units.That of the benzoic ion from the older data, when converted into re- ciprocal ohms, is 32 to 33. Some values for the molar conductivity of sodium benzoate up to a dilution of 1024 litres are to be found in the literature and from these and the values formerly obtained an extrapola- tion of the A, Jc graph leads to ho = 85. The increase in molar con- ductivity between V = 1024 and V = 00 may be estimated in the analogous case of sodium acetate from the molar conductivities at 18" and the temperature coefficients of ionic conductivities. I t is found to be 3.04, and if the increase is the same for sodium benzoate, the values of A, will be 8 ; (Euler) or 83.5 (Schaller). Combining these results with Lo for Na = 5 2 - 3 (Bredig) or 50-9 (Noyes and Falk), we obtain for the benzoic ion, mobilities of 31-2 or 32.5 or 34.In a recent paper by Lorenz and Scheuermanns the value of A, is given as 84.8 (sodium benzoate) Lo for Na. as 5 2 -3, hence Lo for C6H5 COO' is 32 -5. 1 Zeit. Phys. Chcm., 1910, 68, 459. 3 Zeit. anorg. Chem., 1921. Far. SOC., loc. cit.BENZOATES AND SALICYLATES 39 Salicylic Acid. The difference between the X values of sodium benzoate and salicylate We have taken the mobility of the The transport numbers of the anions, then, will be calculated from the Na. 51.0 K. 74.5, C,H,COO' 33.0 C,H,OHCOO' 36.0 Sodium benzoate Potassium benzoate Potassium salicylate at V = 1024 is 2-7 (Ley and Euler). salicylic ion as 36 in round numbers. following mobilities :- %A = 0'394 0.307 0.326 Transport Numbers and Dzyhsion Potentiah.In the usual formula which gives the diffusion potential Ed = ( I - 2n,)RT/nF log C,/Cz, the ionic concentrations were formerly taken as effective mobility concentra- tions in which the coefficients a contain the assumption that the whole diminution in conductivity is due to decreased ionisation, the actual velocity of such ions as exist remaining the same. I t is now generally, although not universally, considered, that the ion concentrations derived from conductivity should be corrected for viscosity and, introducing this correction in its simplest form, the ion concentrations are : a,r,C, in which uK is the conductivity degree of dissociation and q is the relative visc0sity.l It will be noticed that the divergence between a, of sodium and potassium benzoates at the (corresponding) higher concentrations is due to the higher viscosities of the sodium benzoate solutions according to this view.The ratios of the corrected ion concentrations, a,ylCJ2a,q2C2 over the range examined are actually almost identical with those of the total concentration C,/C,. From the tables it will be seen that log c,/c2 = log a,y,C,/az& except for a small correction which must be added to the left log ratio when - log C, is greater than 1.5 and - log C, is less than 1.5. For sodium benzoate, - log aC = - log C+ 0.09. For potassium benzoate, - log aC = - log C + 0.08. Viscosities The viscosities are known of solutions of many sodium salts but of few potassium salts. Those of potassium benzoate were determined in the Ostwald-Poiseulle viscometer at 25'.They are close to those of sodium benzoate to about C = 0-2, and from this point become much lower with increasing concentration. The graph of 7 against C has an inflection. From it we have obtained the intermediate values of 77. ReZative Viscosities of Potussizm SoZutions a t 2 5 '. C = 0.1 0 . 2 0'3 0.4 0.5 0.6 0-7 0.8 0.9 1.0 q = 1-058 1,107 1.139 1.870 1.204 1.249 1.294 1-347 1-401 17460 1 See Kraus and Bray, 3'. Amer. Chem. SOC., 1913, 35, 1315 ; Bousfield, Far. SOL. Trans , 1919, 15, Pt. I., 50 ; Lewis and Randall ( ( Thermodynamics," p. 315.40 DIFFUSION POTENTIALS AND IONIC MOBILITIES OF 0.877 1-756 1.752 1-01 TABLES. The values at different concentrations of :- Equivalent conductivity, conductivity degree of dissociation a K , viscosity q, log of ion concentration derived from conductivity log a&, log of ion concentration corrected for viscosity log aC. Sodium benzoate at 25', A, = 85.0.879 1.862 - - c = 1'00 -log c = 0'00 A = 42'0 aK = 0'495 r] = 1'65 -log aKC = 0'306 -log aC = 0.0885 C, and C, = N and N/4 N and N/6 N and N/8 E ~ = I I * ~ I 16.60 18'48 0.856 and 0,0856 C, and C,=N and N/3o Ea=31*8 23.0 0.5 0.301 52% 0'619 1-28 0'509 1 Oe402 N and N/ro N and N / I ~ N and N/2o 27-84 - 18.78 23'40 - - - - 0 -2 0.70 0'73 0.836 62'0 1'12 0'787 0'1 I ' O O 67'2 0'79 1-05 1.081 1'102 0.05 1.30 0'83 1'03 1'382 70'4 1'369 0.03 12 1'505 0.851 1'015 1.575 1.570 72'4 0.0078 2.105 0'907 2'149 77'0 - - Potassium benzoate, A, = 107. 0-50 0.301 73'94 0.69 0.462 0.381 0.25 0'602 80'44 0'75 0.726 0.6835 0.125 0.g03 0.808 86-86 1-00 0.965 0.0625 1.204 0'84 1-280 1'262 89-92 0'03122 1.505 0.88 1.561 1.552 94'0 1 By analogy with the corresponding value for sodium benzoate.Th Dzfusion Potentials. These have been measured under conditions as comparable as possible with those of the membrane potentials, in order to obtain independent values of the transport numbers, which can be compared with those deduced from the ionic mobilities. Two saturated KCl calomel half-cells when connected through saturated KCl gave either no potential difference, or a reversible one of the order of a millivolt, which was allowed for. The main bulks of all solutions were immersed in a thermostat at 25O. The diffusing surfaces between the two solutions were made and renewed in a special apparatus which could also be adapted to give flowing junctions. The sketch of the part containing this surface (Fig.2 ) shows that the more con- centrated solution C, and the more dilute C, can be run through in different ways, so as to form fresh surfaces either at d or e orf; that at d being the sharpest. The diffusion at this surface was measured through tubes filled with the solutions C, and C, and connected by salt bridges, etc., with the calomel half-cells. By an alteration in the connecting tubes a flowing junction can be set up at$BENZOATES AND SALICYLATES 41 E = a + b log C,/C,, the coefficient b when divided by 59 gives the value of I - Z ~ A characteristic of the series. Ed = - 0.5 + 21-13 log C1/Cz Hence 1 - 2nA = 0'3575, nA = 0'321. The last value in the table was obtained by one of us from another solution and gives I - 2nA = 0.39, BA = 0.305.50 40 30 t 2o E KB. I0 0 t E KS The diffusion and membrane potentials of potassium benzoate and salicylate. E in mv, potassium benzoate, 0. Fig. I E in mv, potassium salicylate, X. FIG. 2.42 DIFFUSION POTENTIALS AND IONIC MOBILITIES OF C, and C, = 0.87 and 0.29 C, and C, = 1.0 and 0.1 C, and C, = 1.0 and 0.033 Ed = 10.1 Ed = 21'2 Ed = 31'5 Potassium SaZicyZa te a t 2 5 '. 0-55 and 0.137 12.7 0.823 and 0.0585 24'5 0'55 and 0*0112 30.0 0.55 and 0.11 15.1 1.0 and 0.05 29'3 1-0 and 0.02 37'8 0'87 and 0.124 18 -0 1.0 and 0.04 29.1 Hence Ed = 0.26 + 20.9 log C1/C2. I - 2 n ~ = 0.3536. Sodium Benzoate a t about I 8". The measurements already referred to have been recalculated, with the 1-0 and 0.1 substitution of log Cl/C2 for log Cl/C,. C, and C, = 0.1 and 0.01 Ed = 12'8 C, and C, = 1.0 and 0.02 0.5 and 0.01 I 1.0 y5d1o*or 21'2 12-85 - I - - Ed = 22'60 1 - Hence Ed = 12-43 lOgCJC2, I - 2 1 ~ ~ = 0'2154.By the substitution of log a,& for log C in the least squares calculations we obtain the following constants :- Sodium benzoate, a = 1.085, b = 11-73, I - 2nA = 0'202 I - znA = 0'3 7 3- Potassium benzoate, a = 1.78, b = 22.03, Summary of Transport Numbers. 1 Sodium Benzoate. ~ Potassium Benzoate. K Salitylate. From,LAandOLK . . From Ed, c,, C, . . . From Ed, U , T ~ C , and a2v9C2 . I 0'394 0.307 0.392 0.32 I 0.399 0.313 0.326 0.323 - The Membrane Potentials. Flanged glass tubes bearing annular rubber washers and clipped together with brass plates and screws held the parchments tightly against the pressures of the columns of liquids.The membranes consisted of four thicknesses of parchment paper (of the kind used for dialysis experiments) set horizontally in vertical tubes. (Note.-In the former research a horizontal membrane consisting of one thickness of parchment was used. We have found that the same results can be obtained with either arrangement.) The two sides of the parchment were connected with reservoirs delivering the more concentrated solution just below the membrane and the more dilute just above. These upper and lower surfaces were connected through siphons and taps with the saturated KC1 calomel electrodes. The potentials were tested by running either or both solutions at different rates, and slight fluctuations were ob- served in some cases according to whether the solutions were still or moving.There is in all cases a slow diffusion, and therefore the fall ofBENZOATES AND SALICYLATES 43 C, and = N and N/4 N and N/6 log C,/C,l = 0.5998 0'7728 C, and C, = N and N/16 En, = 17-70 21-69 log C,/C, = 1'1936 1.346 E, = 37-41 38'64 N and N/20 concentration does not take place completely in the membrane. A small part of the potential is therefore a diffusion potential and consequently the observed is a little lower than the true membrane potential. With a four- fold membrane, judging by the magnitude of the fluctuations mentioned above, this effect is only slight. From time to time samples run off from sides of the membrane were analysed in order to determine the actual con- centrations of the solutions at the times of measurement.The parchments were steeped for at least several hours in distilled water before the tubes were refilled with fresh solution. These requirements make the measure- ments rather slow; no more than two or three were done in a day. In the tables there have been included the membrane potentials of sodium benzoate recalculated with the substitution of log Cl/C, for log alCl/a2C2. Applying the method of least squares to these and the other results, we obtain a formula similar to that already given ; the symbols being distinguished by the subscript " m." Em = a + b log CI/C,, b = 59(1 - 2 , ~ ~ ) . N and N/8 N and N/IO N and N/14 0-9052 0.9973 I '1 274 N and N/3o 32'68 - 27-13 -. 27'55 44-06 - - - - 1.4578 Sodium Benzoate.C, and C, = 0'202 and 0-1007 C, and C, = 0.505 and 0'064 C, and C, = 0*202 and 0-012 Em = 10.8 Em = 24-20 Em = 35.1 - 0'505 and 0*209 0'202 and 0.021 28.25 1'0x0 and 0.023 3 7'25 12'2 .tLm = 5-34 + 21-14 0.202 and 0'064 14-95 0.501 and 0.0252 32.6 - 0.202 and 0'025 23-05 0.505 and 0'0245 34'45 - Potassium B e nzoa te. C, and C, = N/IO and N/20 log cl/c2 = 0.2954 Em = 11.5 Poiassium SaZicyZate. N and N/3 N/7 and N/28 N/3 and N/15 N/7 and N/42 0.4690 1 0;:; 1 0;36852 1 0.766 13'1 24-6 C, and C, = N and N/7 log C,/C, = 0.8313 E m = 25'3 C, and C, = N and N/2o log CJC, = 1'2853 Em = 441'8 I ---.I I I 1.080 1.165 I I- I I44 IONIC MOBILITIES OF BENZOATES AND SALICYLATES Potassium Benzoate. From these results a new transport number of the anion ,,pa can be obtained, which should give the relative mobilities of the ions in the membrane.Potassium Snlicylate. Sodium Benzoate. 0'5036 0.516 0.248 0.242 0'77 We attribute the decrease in the transport number of the anion chiefly, if not entirely, to a decrease in its mobility. This may be due to the larger diameter of the anions, or to a preferential adsorption of the anion on the parchment, although this material was chosen partly on account of its freedom from specific adsorption or chemical effects. Whatever may be the mechanism, we shall try to express the facts by means of a diminution of u, in some ratio '' r." On the above hypothesis the mobility of the anion should be diminished in the same ratio, whether it is present in a sodium or in a potassium salt (benzoate). A different ratio may be found for another anion (salicylic). Using the values of u, etc. given above, and writing for the mobility in the membrane ,uA its substitute ru,, the following equations will de- termine '' Y." Sodium Benzoate. 0'318(51 f 33T) = 33Y, Y = 0.725. Po f assizcm Benzoate. 0'248(74'5 -l- 33Y) = 33r, r = 0'745. Potassium SaficyZate. 0'242(74'5 4- 36r) = 36r, = 0.66. On this hypothesis, therefore, the parchment reduces the mobility of the benzoic ion in the ratio 0.735 and that of the salicylic ion in the ratio 0.66. In conclusion, one of the authors (E. B. R. P.) desires to acknowledge a grant from the Royal Society with which some of the apparatus was purchased, Owing to various causes this work, for which the grant was allotted, could not be completed until the present. Universify Co ZZege, No ftingham.

ISSN:0014-7672    

DOI:10.1039/TF9242000037

出版商:RSC    

年代:1924

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. INVESTIGATION ON OPPAU AMMONIUM DISCUSSION . . 78-83 SULPHATEMN ITRATE INTRODUCTION. By Sir Richard Threlfall, K.B.E., F.R.S. . INVESTIGATION ON THE CHEMICAL AND PHYSICAL PROPERTIES OF OPPAU AMMONIUM SULPHATE-NITRATE AT THE GOVERN- MENT LABORATORY. By Sir Robert Robertson, K.B.E., F.R.S., Government Chemist . Appendix I. OPTICAL EXAMINATION OF CERTAIN PREPARATIONS CONTAINING AMMONIUM SULPHATE AND AMMONIUM NITRATE. By Dr. H. H. Thomas and Mr. A. F. Halli- mond . Appendix 11. X-RAY EXAMINATION OF OPPAU SALT. By Sir William Bragg, K.B.E., F.R.S. . REPORT ON EXPERIMENTS TO DETERMINE WHETHER AMMONIUM SULPHATE-NITRATE AS PREPARED AT OPPAU POSSESSES EXPLOSIVE PROPERTIES. By Godfrey Rotter, O.B.E., D.Sc., Director of Expiosives Research, Woolwich VACUUM STABILITY TESTS ON OPPAU SALT AND . Appendix I. AMMONIUM NITRATE . Appendix 11. ATTEMPTS TO INDUCE EXPLOSION OF OPPAU SALT BY THE APPLICATION OF A DETONATIVE IMPULSE Appendix 111. ATTEMPTS TO INDUCE EXPLOSION OF OPPAU SALT BY INTENSE LOCAL HEATING . Appendix IV. EXPERIMENTS WITH DETONATIVE IMPULSE UNDER HEAVY CONFINEMENT . Appendix V. EXAMINATION OF SAMPLES OF ASTRALITE AND PERASTRALITE . PAGE 46 46 55 59 61 65 66 7 2 74 7 7 45

ISSN:0014-7672    

DOI:10.1039/TF9242000045

出版商:RSC    

年代:1924

数据来源: RSC