426 Dr. J. H. Gladstone and Mr. A. Tribe on the 



ments, employing chloride of copper, and observed some facts 

 which seemed to have an interest from their bearing on the 

 causation of galvanic action. 



It is known that if metallic copper be placed in a solution of 

 cupric chloride, it will slowly become covered with a crystalline 

 deposit of the insoluble cuprous chloride : — 



Cu + CuCl 2 =2CuCl. 



We found that when metallic copper and platinum are con- 

 nected by a wire and immersed in cupric chloride, the insoluble 

 salt forms not only upon the copper, but also on the platinum 

 plate, as a white crystalline body. This deposit may generally 

 be observed in about two minutes when the plates are three 

 quarters of an inch apart. The formation of cuprous chloride 

 upon the platinum plate takes place about equally rapidly in 

 solutions containing 2*5 or 10 per cent, of salt. With a 20 per 

 cent, solution the deposit was smaller, and with 40 per cent, 

 practically nil, although there was abundant formation of cu- 

 prous chloride upon the copper plate. 



We satisfied ourselves that the action took place equally well 

 in solutions from which oxygen had been rigidly excluded, and 

 also that a current passed from the copper to the platinum 

 through the liquid — that is, from the metal of higher to that of 

 lower potential. 



In order to test whether this electrolysis of cupric chloride into 

 CuCl and CI could be effected by weak currents ab extra, we tried 

 the effect of a zinc-platinum cell excited by common water and 

 with platinum electrodes, and found that cuprous chloride depo- 

 sited upon the negative electrode and chlorine at the positive, a 

 little of which entered into combination with the platinum, but 

 the greater part passed into the liquid. A cell excited with 

 dilute sulphuric acid acted in a similar mamier. A single Grove's 

 cell gave for the first two or three minutes cuprous chloride on 

 the negative platinum electrode, but afterwards metallic copper, 

 while chlorine always formed at the positive plate. 



As zinc immersed in a salt of copper is capable of throwing 

 down that metal, an experiment was tried with plates of zinc and 

 platinum in connexion immersed in the chloride ; the result was 

 a more energetic action than with a copper-platinum couple simi- 

 larly arranged, and besides a thick coat of cuprous chloride the 

 edges of the platinum were incrusted with metallic copper. A 

 similar magnesium-platinum couple gave a similar result, but 

 with a decidedly greater proportion of metallic copper. 



As there are two chlorides of mercury, similar to the two chlo- 

 rides of copper, analogous experiments were tried with solution 

 of corrosive sublimate. 



