256 Dr. Faraday's Experimental Researches in Electricity. 



ter (707.); for then the hydrogen evolved from the acetate at 

 the cathode is always found to be definite, being exactly pro- 

 portionate to the electricity which has passed through the so- 

 lution, and, in quantity, the same as the hydrogen evolved in 

 the vol ta- electrometer itself. The appearance 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-chemical action, 

 except by a circuitous process (843.). In place of oxygen, or 

 even the gases already described (74-9.), peroxide of lead now 

 appears at the positive, and lead itself at the negative elec- 

 trode. 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 results 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. 



751. 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 nega- 

 tive 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 separated 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 evolution with an acid more dilute. The 

 gas at the anode was always oxygen; that at the cathode hy- 



