GALVANIC COPPERING. 81 



a thick paste of fluor-spar and oil of vitriol, exposing it for 

 24 hours to a temperature of 59° to 68°, and then washing it 

 off with water. If the surface was not rough enough, the 

 operation was repeated. The rough surface was rendered 

 conductive by brushing on it well-ignited graphite powder, 

 and then coppered by a Daniell's battery. Liquids were 

 boiled in this vessel without loosening the copper coating. By 

 coating a capsule with a varnish, bronzing it, precipitating 

 copper on it, and then loosening the copper coating by heat, 

 this copper vessel may be silvered or gilded, and found useful 

 in the laboratory. 



G-alvanic Coppering. — For coppering smaller articles of 

 iron, zinc, &c., a solution of cyanide of copper, dissolved in 

 cyanide of potassium, is employed. The experiments of 

 Rammelsberg (Pogg. Annal. vols, xxxviii. and xlii.) prove that 

 two chemically distinct compounds exist, one consisting of 

 1 equiv. each of cyanide of potassium and cj^anide of copper, 

 the other of 3 equiv. cyanide of potassium, and 1 equiv. cy- 

 anide of copper. The former is difficultly soluble, crystal- 

 lizes in needles, and, when treated with cold water, is resolved 

 into white insoluble cyanide of copper : the latter is quite 

 soluble and crystallizes in rhombs. Both salts are formed in 

 the usual way of preparing the coppering liquid, which is 

 made by adding cyanide of potassium to a solution of blue 

 vitriol or verdigris, until the precipitate redissolves. For 

 upon evaporating the solution, the needles crystallize out 

 first, and then the more soluble rhombs. 



According to BiJttger's experiments, the soluble salt pro- 

 duces the finest coppering, and for ordinary purposes it is only 

 necessary to digest copper-ash (a mixture of copper, oxide, 

 and suboxide^ with a concentrated solution of cyanide of po- 

 tassium (1 pt. cyanide to 6 pts. water) for ^ an hour, at the 

 temperature of 190°, to filter and dilute with aa equal volume 

 of water. To obtain the soluble salt, pure metallic copper 

 (precipitated by zinc) is dissolved in a solution of cyanide of 

 potassium. The oxides of copper give rise to the insoluble 

 salt. (Polytech. Notizbl. by 11. Biittger, 1846.) 



