164 Eledrography. 



ing granulations over its whole surface, each inequality answer- 

 ing to a similar one on the membrane. 



These facts may be important in the practical use of this art, 

 where success depends on the beauty of the result. 



Mr. Spencer remarks, that in these experiments the zinc should 

 never be amalgamated, notwithstanding the great advantage of 

 that mode of treating zinc in other Voltaic arrangements. Our 

 experience, on the other hand, has shewn us that there are advan- 

 tages in adopting this method, and the results which v/e have 

 obtained with amalgamated zinc, have been very good. 



The phenomena attending this process are interesting. It has 

 been long known that in the electrolysis of a metallic salt, both 

 the salt and the water of the solution are decomposed. In this 

 case the sulphate of copper is at first resolved into sulphuric acid 

 and oxide of copper, and the water also into its elements. 

 The sulphuric acid being electro-negative goes over to the zinc- 

 ode, whither the oxygen of the decomposed water has also gone. 

 Here the oxygen unites with the zinc to form the oxide of that 

 metal, which is instantly dissolved by the free sulphuric acid, 

 forming sulphate of zinc. But the hydrogen liberated from the de- 

 composed water all goes to the platinode, where, finding the oxide 

 of copper, it unites with its oxygen to form water, and the metal- 

 lic copper is deposited, according to its own laws of crystallization, 

 on the nearest metallic surface in the Voltaic circuits. Hence the 

 art which forms the subject of this article. It must also be re- 

 membered that the same phenomena attend the zincode of this 

 series that we have described as belonging to the copper or plati- 

 node, namely, water is there decomposed, the oxygen forms ox- 

 ide of zinc, and the hydrogen goes to reduce the oxide of cop- 

 per, unless indeed, there is an excess of sulphuric acid in the 

 zinc cell, in which case, free hydrogen will be evolved from 

 that cell. The deposit of metallic copper is an exact equivalent 

 for the oxidation of the zinc. Indeed no deposit can take place 

 until the zinc is oxidized, and hence the necessity of a free acid 

 or saline fluid in the zinc cell, to commence the decomposition. 



Much light has been thrown by these experiments and those of 

 Mr. Fox on the mode in which metallic deposits occur in nature. 

 But at this time we can only mention the subject; to treat of it 

 would require more space thau we can at present command ; we 

 postpone it therefore to some other occasion. B. S., Jk. 



Yale College Laboratory, Dec. 23(1, 1340. 



