356 KEPORT— 1888. 



the constituent atoms or ions ; the change appears to me to he precisely of the 

 character of that which occurs when ice suddenly liquefies at 0°, and may equally 

 be regarded as the result of a sudden alteration in molecular structure. 



I will only add that I have attempted to take into account the properties of 

 matter in all states, not merely the state of extreme dilution. 



The following remarks by the Chemical Secretary, Dr. Armstrong, 

 are appended, in order to direct attention to what he considers the un- 

 certainty in which our conceptions of the fundamental phenomena of 

 electrolysis are still enshrouded, notwithstanding the very definite asser- 

 tions of recent foreign workers : — 



There can be no doubt that the work done during the past year — which in many 

 •ways has been one of remarkable activity' — has tended more and more to favour 

 the acceptance of the dissociation theory of electrolysis, that the conviction has 

 been strengthened that electrolysis is primarily an affair of atoms : indeed, so far 

 has this idea gained ground, that it is even argued by Arrhenius, whose conclusions 

 are accepted by Ostwald and others, that in dilute solutions of hydrogen chloride, 

 for example, as much as 90 per cent, of the HOI is dissociated into its ions. Prof. 

 J. J. Thomson, in his recent work, ' Applications of Dynamics to Physics and 

 Chemistry,' has, I think, very happily criticised this conclusion in the following 

 passage (p. 213) : — 



' The reasons given for this conclusion do not seem to me to be very convincing, 

 and the experimental results on which they are based seem to admit of a very 

 different interpretation. The supporters of this theory urge that, for the salt to 

 produce the etiect which in some cases it does, it is necessary to suppose that the 

 molecules of the salt exert a greater pressure than they would if they occupied the 

 same volume at the same temperature when in the gaseous condition. This 

 reasoning is founded on the assumption that all the effects due to the dissolved 

 salt m'ay be completely explained merely by supposing the volume occupied by the 

 solvent to be filled with the molecules of the salt in the gaseous condition. Now, 

 though we may admit that the salt does produce the etfects that would be pro- 

 duced by this hypothetical distribution of gaseous molecules, still it does not follow 

 that these are the only effects produced by the salt. The salt may change the 

 properties of the solvent, and the effects attributed to the dissociation of the 

 molecules may in reality be due to this change.' 



Deville, who studied the behaviour of hydrogen chloride at high temperatures 

 by means of his well-known apparatus with an internal cooled tube, observed only 

 traces of dissociation at 1300°, and Crafts and F. Meier could detect no appreciable 

 dissociation in porcelain vessels at 1500°, although in platinum at about 1700°, 

 according to Victor Meyer and Langer, it is to a considerable extent resolved into 

 the component elements. That a gas of such stability shoidd be almost entirely 

 dissociated by mere dissolution in water is to me incredible. 



Apart from actual electrolytic studies such as those of Arrhenius and Ostwald, 

 the most important influence in forming opinion has been exercised (a) by van 't 

 Hoff's masterly generalisation {cf. ' Phil. Mag.,' 1888, 26, 81), to which Prof. J. J. 

 Thomson is referring in the above-quoted passage, that the molecules cf dissolved 

 substances in dilute solutions exert the same pressure as they would if theywere 

 in the gaseous state at the same temperature and volume ; and (6) by the intro- 

 duction of Raoult's method of ascertaining molecular weights of dissolved sub- 

 stances by determining the extent to which they depress the freezing-point of the 

 solvent {cf. ' Chemical Society's Transaction.s,' 1888, 610). While recognising the 

 beauty of the conceptions, and while ready to admit that tliey may be applicable in 

 many cases, my opinion is very much that expressed by Prof. J. J. Thomson. I 

 agree with him that it is both possible and probable that a change in the constitu- 

 tion of the solvent is effected by the dissolved substance {cf. ' Chemical Society's 

 Transactions,' 1888, 125). The extraordinary effect on the properties of gold and 

 copper, for example, of small amounts of certain foreign matters, so well known to 



' Cf. OstwEld and van 't Hofi's ZcHschrift fiir phygihalische Chemie. 



