Primary and Secondary Results of Electrolytic Action, 253 



stinction, already recognised among scientific men, relative to 

 the products of that action, namely, their primitive or second- 

 ary character; and, if possible, by some general rule or prin- 

 ciple, to decide when they were of the one or the other kind. 

 It will appear hereafter that great mistakes respecting electro- 

 chemical action and its consequences, have arisen from con- 

 founding these two classes of results together. 



743. When a substance under decomposition yields at the 

 electrodes those bodies uncombined and unaltered which the 

 electric current has separated, then they may be considered 

 as primary results, even though themselves compounds. Thus 

 the oxygen and hydrogen from water are primary results ; 

 and so also are the acid and alkali (themselves compound 

 bodies) evolved from sulphate of soda. But when the sub- 

 stances separated by the current are changed at the electrodes 

 before their appearance, then they give rise to secondary re- 

 sults, although in many cases the bodies evolved are ele- 

 mentary. 



744. These secondary results occur in two ways, being 

 sometimes due to the mutual action of the evolving substance 

 and the matter of the electrode, and sometimes to its action 

 upon the substances contained in the decomposing conductor 

 itself. Thus, when carbon is made the positive electrode in 

 dilute sulphuric acid, carbonic oxide and carbonic acid appear 

 there instead of oxygen; for the latter, acting upon the matter 

 of the electrode, produces these secondary results. Or if the 

 positive electrode, in a solution of nitrate or acetate of lead, 

 be platina, then peroxide of lead appears there, equally a 

 secondary result with the former, but now depending upon an 

 action of the oxygen on a substance in the solution. Again, 

 when ammonia is decomposed by platina electrodes, nitrogen 

 appears at the anode * ; but though an elementary body, it is a 

 secondary result in this case, being derived from the chemical 

 action of the oxygen electrically evolved there, upon the am- 

 monia in the surrounding solution (554.). In the same man- 

 ner when aqueous solutions of metallic salts are decomposed 

 by the current, the metals evolved at the cathode, though ele- 

 ments, are always secondary results, and not immediate con- 

 sequences of the decomposing power of the electric current. 



745. Many of these secondary results are extremely valu- 

 able; for instance, all the interesting compounds which M. 

 Becquerel has obtained by feeble electric currents are of this 

 nature; but they are essentially chemical, and must, in the 

 theory of electrolytic action, be carefully distinguished from 



* Annates de Chimie, 1804, torn. li. p. 167. 



