92 REPORT— 1891. 



H + CI + K + OH = CI + K + H^O 

 and 



H + NO3 + Na + OH = NO3 + Na + H^O 



be of different thermal value, one molecule of water being 

 formed in each case from hydrogen and hydroxyl ? Such 

 thermal differences as are found in different neutralisations 

 are accounted for by different degrees of dissociation. 



From the purely chemical point of view a good deal may be 

 said effectively in favour of this, to chemists, at first sight 

 startling hypothesis. How is it that alcoholic solutions of 

 ethyl chloride, ethyl iodide, ethyl sulphide, do not give precipi- 

 tates of the silver salts when treated with silver nitrate ? Why 

 should they not, when solutions of metallic chlorides, iodides, 

 and sulphides give the reaction so readily ? Surely KCl, which 

 is so stable a compound, should not break up more easily than 

 one in which CI is united to carbon ? And yet it does ; and 

 the explanation now offered is that KCl is not a stable com- 

 pound when treated with solvents, but an exceedingly unstable 

 one, while CoH.Cl proves itself to be stable by its refusal to 

 yield CI to Ag. Chemists must be careful as to the use of 

 that word " stable." They are rightly accustomed to regard in- 

 ertness at high temperatures — a resistance to the disintegrating 

 influence of heat — as a proof of stability ; and yet it is a common 

 thing to speak as if the very opposite quality of great activity 

 — or tendency to decompose under the influence of material 

 agents in solution — were a sign of that same quality. Perhaps 

 this is because the two properties often enough go together. 

 Thus KCN is inert at very high temperatures, but is decom- 

 posed in solution by the weakest of acids, while AgCN breaks 

 up easily on heating, and resists the action of acids. Which is 

 the more stable cyanide ? I fancy that depends on the special 

 conditions, w^hich must be defined before the answer can be given. 

 According to the new ideas, the strongest acids and bases are 

 the most dissociated in solution, and their strength depends on 

 this fact, while weak ones like acetic acid are stable enough. 

 And we are now to conceive that most of the reactions on 

 which we are accustomed to rely in analysis — what may be 

 called double decompositions in the wet way — involve the 

 union of free ions, and not the interaction of compound mole- 

 cules. Chemists have long recognised that such processes 

 never give us a general test for an element, but only tests for 

 the metals and radicles of salts — and that means the ions of 

 electrolytes. Apparently, we must change our ideas about 

 double decomposition, since the phrase itself is now a mis- 

 nomer. 



A relation between the degree of dissociation and the con- 

 ductivity of an electrolyte obviously exists, since the strong 



