338 Mr Con nell on the Action of 



influence on that body. I have compared dilute sulphuric acid 

 of a given strength, with the same acid of different strengths, 

 with alkaline solutions, and with solutions of alkaline sulphates, 

 by transmitting the same electric stream through them, and have 

 found that the quantity of hydrogen evolved from the negative 

 pole was always, with trifling deviations, a fixed quantity for the 

 same current. The quantity of oxygen separating at the positive 

 pole was subject to those variations from the absorption of the 

 fluid, which Mr Faraday has pointed out ; but the quantity in 

 one experiment with another was evidently such as corresponded 

 with the hydrogen evolved, after allowing for the absorption. 



It is evident how important an aid this principle affords us, in 

 explaining what passes during the electric decomposition of 

 aqueous solutions ; for if, in comparing with one another, solu- 

 tions of substances of different atomic constitutions, we obtain 

 hydrogen or oxygen, or both, in the proportions contained in 

 water, we have strong grounds for concluding that the solvent, 

 and not the matter dissolved, has been the subject of decomposi- 

 tion. 



Accordingly, it is in this way that we are enabled to determine, 

 with every appearance of probability, that in a great many, per- 

 haps in all cases of solutions of the oxyacids, water only is the 

 subject of direct voltaic decomposition. Thus the same voltaic 

 current was passed through dilute sulphuric acid, and a solution 

 of boracic acid, and it was found that very nearly the same rela- 

 tive quantities of hydrogen and oxygen were evolved from both 

 solutions in the same time, notwithstanding the difference in the 

 atomic constitution of the two acids. There was, therefore, little 

 doubt that, in both solutions, the water, and not the acid, had 

 suffered decomposition. Iodic acid appeared to me to be ex- 

 tremely well calculated for such an experiment, as the feeble 

 affinity by which its elements are held together, afforded the 

 most favourable circumstances for a direct decomposition of an 



7 



