AQUEOUS AND ALCOHOLIC SOLUTIONS. 1 61 



hydracid salt, instead of supposing the secondary action of hydrogen on the haloid, 

 and reaction of the metal on water. 



We cannot easily get the same direct evidence on this subject by the method 

 applied to aqueous solutions, of placing the poles in water beyond the solution, 

 because, from the inferior conducting power of the alcoholic solution, less acid 

 will be separated, if it truly exists, in the liquid ; and we cannot distinguish 

 whether it may not come from the point of junction of the alcoholic solution with 

 the water in which the poles are placed. Hence, I believe that, in formerly con- 

 trasting the results with alcoholic and with aqueous solutions, the conclusion that 

 no acid was formed in the former solution was incorrect ; and I think it more 

 likely that the acid formed was confounded with that from the point of union. It 

 is fortunate that there is no real need for this illustration in proof of the decom- 

 position of water by haloid salts. 



If alcohol dissolves haloid salts as hydracid salts, there can be little doubt 

 that pyroxylic spirit does the same : I incline to think that the greater solvent 

 powers of the latter fluid than the former in regard to some substances, such as 

 barytes, is due to its greater absolute quantity of water, although not greater 

 atomic proportion. 



V. On the Conducting Power of Solutions. 



Without going the length of holding that the additional conducting power 

 bestowed on water by dissolved substances, is exactly proportional to the degree 

 of chemical change, under voltaic action, resulting from the dissolved body, there 

 seems in every instance in which increased conducting power is bestowed, some 

 chemical change, or at least voltaic transference, attending the increase of con- 

 duction. This chemical change may result either from the direct action of the 

 current or from secondary agencies ; and both circumstances lend their aid, where 

 they occur, in augmenting conducting power. 



In the case of salts, the voltaic separation of acid and alkali at once explains 

 the result, and in many of such cases we have an additional effect from secondary 

 actions at one or both poles. 



Acids alone in solution, as is now generally known, and as I have myself 

 verified experimentally, for sulphuric acid and the hydracids, undergo transference 

 to the proper pole ; which circumstance appears to be the primary cause of their 

 promoting conduction. In some instances secondary actions at the poles also 

 contribute to the result. 



To ascertain whether alkalies have a similar action by suffering transference, 

 a moderately strong solution of caustic potash was placed in a tube B connected 

 as in fig. 3* by asbestos, moistened with distilled water, with two tubes, A and 



* Edin. Trans, xiv. Plate II. 



