ON ELECTROLYSIS IN ITS PHYSICAL AND CHEMICAL BEARINGS. 363 



and its exponent of dilution is not much bigger than 1 [i.e., its conductivity, instead 

 of increasing anything like so fast as concentration, scarcely increases at all]. 

 Kohh'ausch guesses that the cause of this is the prevalence of NH^ in solution 

 instead of NH^HO. Probably dilution increases the supply of NH^HO, and 

 therefore assists conduction almost as much as it for other reasons vfeakens it. 

 This would explain the peculiarly small exponent of dilution. 



(14) The conductivity of anunoniacal solution is caused by a small quantity 



of NH^HO, ivhich is increased by dilution, 



[Surely it is rash to make definite statements like this on such a slender 

 basis of fact.] ^ 



§ 2. Case of acids ; activity. 



Acetic acid has the same properties as ammonia ; so has boracic acid. Tartaric 

 and oxalic have small exponents of dilution. Probably the behaviom* of these 

 acids, as well as of ammonia, is analogous to that of HCl, which only conducts 

 in presence of water. Sulphuric, nitric, phosphoric, behav^e in the same way. 

 Hence — 



(15) The aqueous solution of any hydrate ^ is composed of tivopaHs, besides the 



ivater, viz., an active (electrolytic^ part and an inactive (non-electrolytic^ 

 pai't. The three constituent parts of the solution form a system in 

 chemical equilibrium, such that dilution increases the active and 

 diminishes the inactive pwtion. 



How the inactive and active portions differ is not certain, perhaps only 

 physically ; perhaps the active part is a compound of hydi'ate and solvent. 



To fix ideas we can introduce the notion of a coefficient of activity, defined 

 thus : — 



The coefficient of activity of an electrolyte is a number expressing the ratio of 

 the nmnber of ions which are really in the electrolyte to the number of ions which 

 it would enclose if the electrolyte were totally transformed into simple electrolytic 

 molecules. 



[This ' coefficient of activity ' is evidently the same thing as what, in accordance 

 with dissociation ideas of electrolytic conduction, I called ^ the ' dissociation ratio,' 

 i.e., the relation betvs'een the number of atoms taking part in conduction to the 

 whole number present. It may turn out that this ratio is unity, but it is in any 

 case well to determine it ; and the idea of Arrhenius that it is upon this that 

 chemical activity and rapidity of interchange depends seems to me important.] 



§ 3. Hypothesis of Williamson and Clausius, and consequence 



thereof. 



[The continual interchanges of atoms supposed to occur among the molecules on 

 this view of conduction are here regarded as circular electric currents. References 

 to the original statements of the hypothesis are given as follows : Williamson, 

 Liebig's ' Ann.', vol. 77, p. 37 (1851) ; and Clausius ' Pogg. Ann.', vol. 101, p. 347 



§ 4. Deduction of some electro-chemical laws (16)-(20). 



[^E.<j., Faraday's laws. I omit this section because it is not much use deducing 

 laws like these from an hypothesis. The Williamson-C'lausius hypothesis is of 

 course in harmony with the fundamental laws of the subject, otherwise it would 

 have been pretty soon abandoned. Probably the object of the author is to show 

 how readily the known laws can be built up from one simple foundation.* One 



' See § 7 of letter on p. 386. 



- For ' hydrate ' always read hydrogen compound, either base or acid. 



' On page 756 of last year's B. A. Report, Aberdeen. 



■* gee § 8 of letter on p. 387. 



