ON PYROXYLIC SPIRIT, &c. 135 



most important of these cases are aqueous solutions of the oxyacids, as that of 

 sulphuric acid ; and embracing, as I fully do, his opinion, that the appearance of 

 sulphur at the negative pole in such a case is a secondary result due to nascent 

 hydrogen, I may be allowed to add, that this view seems well illustrated and con- 

 firmed by the experiment which I formerly described, in which the iodine of an 

 aqueous solution of iodic acid appeared at the negative pole, under circumstances 

 in which the secondary nature of the action was quite obvious. 



Mr Faraday, however, made an important exception in the case of aqueous 

 solutions of the hydracids ; but I shall here merely refer to the evidence so fully 

 detailed now* and formerly, which has led me to infer, that in solutions of the hy- 

 dracids, as well as in those of the oxyacids, water only, and not the dissolved 

 acid, is directly decomposed. I have also to refer to the experiment with an 

 aqueous solution of bromide of iodine, from which it appeared that that compound 

 was not directly decomposed when in solution, but only the water, f It would 

 appear, therefore, that we at present know of no combination of two elementary 

 substances with one another, which, when in solution in water, is directly decom- 

 posed by the electric current ; but have every reason to believe, that in such solu- 

 tions the water only suffers direct decomposition. 



Farther, I have endeavoured to shew that in alcoholic solution of acids, al- 

 kalies, and haloid salts, the water of the alcohol alone is directly decomposed. 



The conformity between these views and the results obtained with etherial 

 solutions is remarkable. I formerly stated that no evidence whatever was ob- 

 tained ft'om electric phenomena that ether contained water ; and what was the far- 

 ther observed result? When etherial solutions of potash, of chromic acid, of chloride 

 of platinum, and of corrosive sublimate, were acted on by fifty pairs of 2-inch plates, 

 there neither were any symptoms of decomposition, nor was the galvanometer 

 affected. \ Thus, whilst in aqueous and alcoholic solutions, water and not the dis- 

 solved body is decomposed, in etherial solutions, where there is no water present, 

 no decomposition takes place at all. 



In this way we are arrived within a few steps of the following general con- 

 clusion, Avhich I cannot help thinking, if it shall be fully supported, is one of con- 

 siderable interest, and not I believe hitherto anticipated : " That when solutions 

 of binary combinations of elementary substances, in water, alcohol, or ether, are 

 submitted to voltaic agency, the dissolved substance is not directly decomposed ; 

 but only the solvent, if itself an electrolyte." 



In laying down any general law, which must, if well founded, comprehend 

 a vast multitude of facts, one of course feels the necessity of having proceeded 

 on an extensive induction ; or at least of having established the leading analogies 



* P, 7, et seq. f P. 10. 



f Edinburgh Transactions, vol. xiii. p. 331. 



