96 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



bonic acid. This result of carburetted hydrogen at the positive electrode has a very 

 anomalous appearance, if considered as an immediate consequence of the decomposing 

 power of the current. It, however, as well as the carbonic oxide and acid, is only a 

 secondary result ; for it is the water alone which suffers electro-decomposition, and it is 

 the oxygen eliminated at the anode which, reacting on the acetic acid, in the midst of 

 which it is evolved, produces those substances that finally appear there. This is fully 

 proved by experiments with the volta-electrometer (707.) ; for then the hydrogen 

 evolved from the acetate at the cathode is always found to be definite, being exactly 

 proportionate to the electricity which has passed through the solution, and, in quan- 

 tity, the same as the hydrogen evolved in the volta-electrometer itself. The appear- 

 ance of the carbon in combination with the hydrogen at the positive electrode, and its 

 non-appearance at the negative electrode, are in curious contrast with the results 

 which might have been expected from the law usually accepted respecting the final 

 places of the elements. 



750. If the salt in solution be an acetate of lead, then the results at both electrodes 

 are secondary, and cannot be used to estimate or express the amount of electro-che- 

 mical action, except by a circuitous process (843.). In place of oxygen, or even the gases 

 already described (749.), peroxide of lead now appears at the positive, and lead itself 

 at the negative electrode. When other metallic solutions are used, containing, for 

 instance, peroxides, as that of copper, combined with this or any other decomposable 

 acid, still more complicated results will be obtained ; which, viewed as direct re- 

 sults of the electro-chemical action, will, in their proportions, present nothing but 

 confusion, but will appear perfectly harmonious and simple if they be considered as 

 secondary results, and will accord in their proportions with the oxygen and hydrogen 

 evolved from water by the action of a definite quantity of electricity. 



75 1 . I have experimented upon many bodies, with a view to determine whether the 

 results were primary or secondary. I have been surprised to find how many of them, 

 in ordinary cases, are of the latter class, and how frequently water is the only body 

 electrolyzed in instances where other substances have been supposed to give way. 

 Some of these results I will give in as few words as possible. 



752. Nitric acid. — When very strong, it conducted well, and yielded oxygen at 

 the positive electrode. No gas appeared at the negative electrode ; but nitrous 

 acid, and apparently nitric oxide, were formed there, which, dissolving, rendered the 

 acid yellow or red, and at last even effervescent, from the spontaneous separation of 

 nitric oxide. Upon diluting the acid with its bulk or more of water, gas appeared at 

 the negative electrode. Its quantity could be varied by variations, either in the 

 strength of the acid or of the voltaic current : for that acid from which no gas sepa- 

 rated at the cathode, with a weak voltaic battery, did evolve gas there with a stronger; 

 and that battery which evolved no gas there, with a strong acid, did cause its evolu- 

 tion with an acid more dilute. The gas at the a?iode was always oxygen ; that at the 

 cathode hydrogen. When the quantity of products was examined by the volta-electro- 



