84 ELECTROTYPE PROCESSES. 



depositing the copper. Another method has been proposed, 

 namely, to make a varnish of two parts asphaltum and one part 

 mastic, by fusing these together, and, when cool, dissolving the 

 mixture in spirits of turpentine to a syrup consistence. To pre- 

 vent the deposit coming off the glass, the vessel is first corroded 

 by the fumes of hydrofloric acid. A solution of gutta percha or 

 benzole has also been proposed as a varnish for fixing on the black 

 lead and deposit. 1 



Retorts, basins, and other chemical vessels, are sometimes covered 

 with copper for their protection during boiling and evaporation. 

 China saucepans have also been made and covered with copper to 

 take the place of tinned copper vessels, but the adhesion of the 

 metal upon these substances, even when we attempt to secure it 

 by the means above referred to, is never so perfect but that after 

 a short use the deposit of copper loosens from the vessels. There 

 is then great liability for liquids to get between the coating and 

 the vessel, and when heat is afterwards applied these liquids satu- 

 rated with verdigris boil out. Consequently such coverings are 

 not well adapted, either for culinary purposes or delicate chemical 

 operations. They have, notwithstanding, been highly recom- 

 mended, and the practice of covering the bulbs of large plain 

 retorts, &c., may be useful in a few large manufacturing opera- 

 tions, but our experience is certainly not favourable to their 

 general use. 



On Qalranic Soldering. Among the many applications of the 

 deposition of metals, there is one we have been often asked about, 

 namely, if it would not be possible to solder different metals 

 together by that process. The following article, which we take 

 from the Mining Journal, will give a full reply to all who may be 

 still inquiring for this application : 



" Under the name of galvanic soldering, a process is known by 

 means of which two pieces of metal may be united by means of 

 another metal, which is precipitated thereon through the agency of 

 a galvanic current. This mode of soldering by the ' wet method ' 

 has been often recommended in various periodicals relating to the 

 industrial arts ; but it has been objected that, practically speaking, 

 the union between two pieces of metal could not be effected by 

 means of a metal precipitated by galvanic agency. In order, how- 

 ever, to arrive at a definite conclusion upon this question, M. 

 Eisner undertook the following experiments, the results of which 

 are in favour of the practical use of the operation of soldering by 

 galvanic agency. In conducting these experiments, the kind of 

 battery known as Daniell's ' constant battery ' was employed ; and 



1 Progress of General Science, vol. ii. ; and Pharm. Journal, vol. viii. 



