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. G. A. ELLIOT?' 73 Dr. H. Borns inquired whether Mr. Elliott had also tried the arc method of Langmuir and experimented with Langmuir's flames of atomic hydrogen. Langmuir seemed to consider that the activation was essentially thermal and set in about 1300' C. Mr.W. Taylor asked whether the theory of activation by ionic impact would not have to face the same problems as had been encountered by the theory of activation by molecular collisions. For example, in applying the general equation (6), the quantity K was really thc: rate of formation of activated molecules, which could be considered as an intermediate product in any chemical action taking place. The observed rate of appearance of end-products would depend upon the nature of the subsequent proceed- ings in which the activated molecules were involved, and might well in- volve a further collision frequency, and therefore another power ofp. In addition, there was the loss of activated molecules due to reversion to the normal state. Professor Allmand asked Dr.Lunt whether any work had been done on more complex reactions in which the critical activation energy might be regarded as being shared between two molecules before collision. I n such 674 DISCUSSION a case, the fundamental equation x , = VoE-l would presumably not hold. With regard to Mr. Elliott’s paper, it was of interest that the life of the activated hydrogen appeared to be of the same order as that of Bornhoeffer’s atomic hydrogen. He suggested that the results of an investigation of the activation of chlorine in the electric discharge would be of considerable interest to the photochemist, as the temporary formation of C1, molecules was now being assumed by several workers in discussing the kinetics of the hydrogen-chlorine reaction. Dr.E. 0. Willey (contributed): I t is noticeable that both in Mr. Elliott’s work and also in the earlier experiments of Wendt and Landauer very small yields ofactive hydrogen have been obtained, these never exceeding 0.01 per cent. by volume when the corona or ozoniser is employed. During the course of some recent work by the writer and IDr. E. K. Rideal upon active nitrogen a few experiments were performed with active hydrogen pre- pared by means of the condensed discharge as used in the production of the nitrogen afterglow, and here hydrogen sulphide was obtained equivalent to 0.5 per cent. active hydrogen and at least 0-7 second after the hydrogen had left the discharge. A similar result was obtained when the extent of activation was measured by admitting nitrogen downstream from the dis- charge, ammonia being formed.I t is curious that when this stream of nitrogen was activated also no perceptible yield of NH, was obtained, all other conditions being the same and so it appears probable that the ammonia first formed was under these conditions of experiment decomposed by the active nitrogen present. The frequency of the discharge appears also to be of fundamental im- portance in the production of active nitrogen; the yield of this from a given discharge tube can often greatly be increased by the addition of a condenser of suitable capacity which is connected across the electrodes and appears to “tune” the circuit, so to speak. I t would be of much interest if Mr. Elliott could extend his restarches still further to a correlation of frequency, wave form and the production of active hydrogen, and the circumstances relative to its formation in the H.T.disruptive discharge. Professor Donnan, in reply to the remarks of Mr. Taylor, pointed out that the theory given in the paper was a first attempt to analyse the mechanism of chemical reactions in the ‘‘ silent ” discharge. I t was assumed that any molecule which received a critical energy increment by collision with an electron or ion of sufficient velocity became chemically active, I t was of course, quite possible that a proportion of these active molecules might afterwards become de-activated by collision or by radiation. In its present form, the theory of chemical activation by ionic or electronic collision was stated in the simplest terms, and would doubtless require ex- tension and elaboration.I t had already led to a relationship which agreed in form with that obtained by Mr. Elliott from his results on the activation of hydrogen. Mr. Elliott said that the active hydrogen obtained differed from the monatomic hydrogen of Langmuir, Wood and Bonhceffer in its behaviour in contact with glass wool and tungsten, and at the temperature of liquid air. I t thus resembled the ‘hyzone ’ studied qualitatively by Wendt and others, although Wendt worked with much smaller concentrations than those obtaining in the experiments just described, in which the greatest amounts of active hydrogen observed were of the order of I per cent. by weight. Probably in both cases the active hydrogen consisted of aggregates each comprising one hydrogen atom linked to one-or more hydrogen molecules ; recombination of the active hydrogen to form ordinary hydrogen might therefore be expected to be bimolecular and largely dependent on theC.C. TANNER 75 concentration of the active form. A study of the influence of both wave form and frequency on the production of chemical change in the silent electric discharge was certainly desirable, and they hoped to carry out experiments of this nature very soon. Dr. Lunt explained that the expression for the velocity constant of a reaction, in which chemical change is caused solely by collisions between reactant molecules and ions, was obtained on the assumption that every encounter in which the ion possesses energy equal to, or greater than, Voe, results in the formation of a chemically changed and stable molecule. No attempt had yet been made to derive an equation for more complex types of reaction. The fact that linear relationships, in the form of equation ( 5 ) , leading to definite values of V, had been obtained in the case of active hydrogen, and in the decomposition of nitrous oxide (to be published shortly by Mr. Joshi) was thought to warrant the presentation of the theory in this simple form. It would be interesting to know if Dr. Willey has measured the current and frequency in his condensed discharge experiments. I t is difficult to see in what way a condenser connected across the electrodes could be said to tune the circuit, for any such circuit has a characteristic natural frequency; without a knowledge of the circuit constants it is impossible to predict what influence the condenser would have on this frequency. Generally, it would have the effect of increasing the current across the electrodes, and this current is undoubtedly an important factor in the production of chemical change by an electric discharge.