Co7idiieting Poivers of Solutions. 361 



bestowed on water by dissolved substances is exactly propor- 

 tional to the degree of chemical change under voltaic action re- 

 sulting from the dissolved bodj', there seems in every instance 

 in which increased conductingpower is bestowed some chemical 

 change, or at least voltaic transference, attending the increase 

 of conduction. 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 action 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 their proper pole, 

 which circumstance appears to be the principal cause of their 

 promoting conduction. In some instances secondary action 

 at the poles also contributes to the result. 



To ascertain whether alkalies have a similar action by suf- 

 fering transference, a moderately strong solution of caustic 

 potash was placed in a tube B *, connected by asbestus moist- 

 ened with distilled water, with two tubes, A and C, containing 

 the latter fluid, A being made negative, and C positive by 

 seventy-two pairs of four-inch plates. The whole tubes 

 were covered with a close glass covering, a piece of turmeric 

 paper having been intioduced into the liquids A and C be- 

 tween the asbestus and the poles. In a kw minutes alkali was 

 indicated at the negative pole, and went on increasing during 

 half an hour, whilst the test paper in C was not discoloured, 

 showing that the effect in A was not owing to capillary action. 

 The experiment was then stopped, when the water in A, al- 

 though not alkaline to test paper throughout, became de- 

 cidedly so by concentration, whilst that in C showed no alkali 

 even after concentration. 



In the experiments also already detailed, in which acid and 

 alkali were separately drawn to the poles in distilled water 

 from saline solutions, the alkali usually reached the pole as 

 soon as the acid. 



There can thus be no doubt, that by voltaic action, the alkali 

 in an aqueous solution is transferred to the negative pole. 



Water coloured by bromine gives sensibly more efferves- 

 cence under galvanic action, showing a superior conducting 

 power of the solution. 



The manner in which such simple substances increase the 



» Fig. 2. (p. 243.) 



