1886.] 



Conduction and Molecular Composition, fyc. 



269 



Simple Electrolytes. 



It is undoubtedly a fact that only a limited number of binary 

 compounds are simple electrolytes ; and it is especially noteworthy 

 that, with the single doubtful exception of lique6ed ammonia, no 

 hydrogen compound — whether binary or of more complex com- 

 position — can be classed with the simple electrolytes. Indeed, all the 

 simple electrolytes with which we are acquainted are either compounds 

 such as the metallic chlorides, or metallic salts — nitrates, sulphates, &c. 

 Including metallic chlorides and their congeners and the corre- 

 sponding oxides and hydroxides among salts — regarding water as an 

 acid, in fact — and denying the title of salts — hydrogen salts — to the 

 acids, Hittorf's proposition (" Wied. Ann.," 1878, 4, p. 374): " Electro- 

 lyte sind Salze " may be safely upheld. But only some of the binary 

 metallic salts are electrolytes : beryllium chloride, for example, belongs 

 to the class of "pseudo-dielectrics" (Nilson and Petterson, "Wied. 

 Ann.," 1878, 4, p. 565; Hampidge, "Phil. Trans.," 1883, p. 604) ; and 

 in the case of those elements which readily form two classes of salts — 

 so-called ous or proto-ssdts and ic or ^er-salts, the ous compounds alone 

 appear to be electrolytes. 



It is highly remarkable that whereas fused silver chloride is easily 

 decomposed on passage of a current of low electromotive force, 

 hydrogen chloride is a " pseudo- dielectric" which forms when coupled 

 with the " pseudo-dielectric " water a readily conducting " composite 

 electrolyte;" while mercuric chloride conducts with great difficulty — 

 possibly not at all when pure — not only in the fused state, but even 

 when coupled with water. No explanation of these facts seems to be 

 afforded by ther mo chemical data.* 



The consideration of these and other similar cases, I think, can 



* The following numbers are given by Thomsen as representing the amounts of 

 heat developed in the formation of the specified chlorides in the state of aggrega- 

 tion in which they exist under ordinary conditions (2 x 35*4 grams of chlorine being 

 in each case used in the production of the chloride) : — 



Hydrogen chloride 44,000 units (gram C). 



Silver „ 58,760 „ 



Mercuric „ 63,160 „ 



Stannic „ 63,625 „ 



Stannous „ 80,790 



Lead „ 82,770 „ 



Only three of the chlorides in this list are simple electrolytes. As much more 

 heat is developed in the formation of two of these three — stannous and lead 

 chlorides — than in the case of any of the others, it would appear probable a priori 

 that these would be the most stable ; obviously, therefore, the study of the heats of 

 formation throws no light on differences in electrical behaviour such as are manifest 

 between hydrogen, mercuric and stannic chlorides, ou the one hand, and silver, 

 sianuous and lead chlorides on the other. 



