Dissolution of Gases in Liquids. 43 



substances, and, when pure, they exhibit perfectly constant 

 freezing-points which are depressed by the addition of the dis- 

 solved substance ; and, till some argument to the contrary is 

 forthcoming, I must maintain that I am perfectly justified in 

 talking of them as solvents, and in talking of the depression 

 of their freezing-points. I certainly join issue with Dr. Walker 

 in his opinion that the crystallization of a substance from a 

 liquid does not prove the existence of some molecules of that 

 substance in the liquid (see Chein. Soc. Trans. 18*>0, p. 340, 

 where various reasons against this view, none of which Dr. 

 Walker discusses, are given), although the number of these 

 which are present may be insufficient to be recognized by the 

 methods at our disposal, especially in a case such as that of 

 racemic acid to which he alludes, where only a comparatively 

 weak solution can be investigated. If racemic acid could be 

 fused, and if it was then found that the liquid gave none of 

 the reactions of racemic acid, then Dr. Walker's argument, 

 though, perhaps, not conclusive, would have some weight. The 

 other instance, of ammonium chloride, which he quotes in 

 support of the view that a solid may be obtained from a fluid 

 in which none of the molecules of the former exist, is equally 

 unfortunate, for if Dr. Walker had glanced at the values for 

 the vapour-density of this substance given by Deville and 

 Troost, and by Neuberg, he would have seen that there must 

 be a very large number of undissociated ammonium -chloride 

 molecules in the vapour even at temperatures considerably 

 above that of its vaporization. Dr. Walker must entirely 

 ignore the positive evidence as to the existence of the liquid 

 monohydrate of sulphuric acid afforded by Perkin's work on 

 the magnetic rotary power (Chem. Soc. Trans. 1886, p. 786), 

 and also by van der Willigen on the refractive power, if he 

 is " inclined to look upon " this substance as being merely 

 diluted sulphuric acid. 



The objections which I raised against the dissociation theory 

 on the score of the energy changes postulated by it, Dr. 

 Walker simply shirks, by stating that as they have not been 

 raised by a physicist he need not trouble himself about them. 

 This is all the more extraordinary because the paper of van 

 der Waals, to which I have already alluded, and which was 

 published after my own, gave Dr. Walker a very good 

 opportunity of answering them. My objections were, of 

 course, based on the view that the dissolved substance was 

 supposed to be in a state of freedom and uncombined with the 

 solvent. If, however, such a view is now abandoned, and there 

 is supposed to be a specific and heat-evolving attraction 

 between the ions and the solvent, it is evidently no longer 



