448 On the polarized Co7idition ofPlatina Electrodes. 



minutes in the same way. At the end of that time a deposi- 

 tion of copper was formed upon the negative electrode. A 

 secondary current of only 15° was obtained. This current 

 varied in many experiments from 15° to 21°, as that obtained 

 from the plates in the pure aqueous fluid from 50° to 54°. In 

 general the secondary current in the sulphate of copper was 

 only one third of that developed in the distilled water, after 

 partial electrolysation. When a solution of nitrate of silver 

 was exposed for ten minutes to the action of the battery, a se- 

 condary current varying from 9° to 12° was obtained. With 

 a solution of sulphate of zinc (after the electrolysation of 

 which a mixture of very impure oxide of zinc, and zinc ap- 

 pear upon the negative electrode) the secondary current was 

 20°. Even these currents, feeble as they were, I cannot help 

 attributing solely to the gaseous combinations going on at 

 those portions of the jplatina which remained exposed. The 

 following experiment shows how very small a portion of the 

 platina surface which has been active in the electrolysation of 

 water is sufficient to the pi'oduction of a far greater secondary 

 current than any of those above mentioned. 



The platina plate to be used as the negative electrode was 

 divided into two portions, one of which was one eighth of the 

 whole plate, which itself was not quite half an inch long and 

 but the fifteenth of an inch in breadth. The two divided 

 portions were so placed together during a few minutes' con- 

 nexion with the battery as to form one electrode ; connexion 

 was broken ; a secondary current of 54° was obtained ; seven- 

 eighths of the plate were then carefully and quickly removed ; 

 the curi'ent instantly fell to 30° ; the removed portion was 

 replaced ; the needle was deflected 50°. 



The current resulting from the combinatio7i of the gases 

 oxygen and hydrogen upon the clear platina surface was often 

 sufficient to decomj^ose "water Jbr s^ome minutes. Immediately 

 that the connexion between the two plates was made this 

 singular effect was produced, oxygen streaming up from the 

 negative electrode and hydrogen from the positive. 



5. The water electrolysed does not, as some have sup- 

 posed, assist in the production of a secondary current by the 

 oxygen which it holds in solution after electrolysation inde- 

 'pendently of that portion upon the surface of the positive 

 electrode, as may be proved by changing the solution in 

 which the plates have been active as electrodes of the battery, 

 or by substituting for the positive electrode after electrolysa- 

 tion a fresh platina plate. In the latter case there is no se- 

 condary current. In the former the current will be the same, 

 whether obtained through the partially electrolysed water, 



