86 ELECTROTYPE PROCESSES. 



results obtained in the preceding experiments, that two pieces of 

 metal may be firmly united by means of galvanically-precipitated 

 copper : in a word, that soldering by galvanic agency is perfectly 

 practicable. It will, therefore, be possible to firmly unite the 

 different parts of a large piece of metal, and to make a perfect 

 figure of them by galvanic precipitation of a metal (copper, in 

 ordinary cases). If solutions of salts of gold or silver were em- 

 ployed in as concentrated a form as those of copper above men- 

 tioned, there is reason to believe that galvanic soldering would 

 also result. In fact, M. de Hackewitz states, that in some experi- 

 ments on a larger scale which he undertook, to obtain hollow 

 figures by galvano-plastic means, he had remarked that galvanic 

 union often took place between the pieces operated upon. M. Eisner 

 states, that while conducting the experiments above-mentioned, he 

 remarked that, by employing too powerful a current, the negative 

 electrodes of copper, and even the plate of copper, and ring of the 

 same metal resting thereon, became covered with a deep brown 

 substance, in the same manner as this occurs under similar circum- 

 stances in galvanic gilding, as is well known. After several unsuc- 

 cessful attempts to prevent the formation of this brown coating, M. 

 Eisner found that it was possible to remove it entirely on immersing 

 the articles covered therewith, during a few seconds, in a mixture 

 of sulphuric and nitric acids. By this means the precipitated copper 

 was made to assume its natural red colour. The possibility of 

 practically effecting the operation of soldering by galvanic agency 

 may be explained in a few words, in a theoretical point of view. 

 The article is, in fact, in an electro-negative state of excitation, 

 whilst the zinc operates positively ; the result is, that the faces which 

 are placed opposite each other, when the ring has been cut, are 

 negative ; that is to say, in an electric condition of the same deno- 

 mination. During the progress of the electrolytic decomposition of 

 the metallic salt in solution (sulphate of copper in the above case), 

 the electro-positive molecules of copper which are detached simul- 

 taneously arrange themselves upon the two opposite faces, and in 

 the direction of the break. Now, from the moment that these mole- 

 cules are deposited they constitute, with the piece, a homogeneous 

 mass ; and from that time act negatively upon the copper which is 

 contained in the solution, and again precipitate copper in the form 

 of regulus. This method of operation continues until the space 

 which existed between the two separate pieces of metal is filled up 

 with metallic copper ; in fact, the layers of copper which become 

 deposited in an equal manner upon the contiguous faces of the 

 metal, gradually diminish the distance which separated the latter, 

 until at length the metallic layers which cross in the opposite direc- 

 tion meet each other ; the result being that the whole of the break 



