578 COPPER. 



Chloride and iodide of cadmium are easily crystallized in com- 

 bination with water. 



Sulphate of cadmium forms efflorescent crystals, CdO, SO 3 + 

 4HO ; and forms a double salt with sulphate of potash : 

 Cd O, SO 3 + KO, SO 3 + 6HO. 



Several definite alloys of cadmium have been formed. At a 

 red heat, 100 parts of platinum retain 1 17-3 parts of cadmium, 

 giving a compound Cd 2 Pt : 100 parts of copper retain, at a red 

 heat, 82.2 of cadmium, which approaches nearly the proportion 

 ofCdCu 2 . Cadmium forms an amalgam with mercury, which 

 crystallizes in octohedrons, and consists of 21.74 parts of cad- 

 mium, and 78.26 of mercury, or CdHg 2 . 



SECTION VII. 



COPPER. 

 Eg. 395.7 or 31.71 ; Cu (cuprum.) 



Copper, if not the most abundant, is certainly one of the 

 most generally diffused of the metals. Its ores are often accom- 

 panied by metallic copper, crystallized in cubes or octohedrons. 

 The richest mines of this country are those in Cornwall and 

 Anglesea. The common ore of this metal is copper pyrites, a 

 compound of subsulphuret of copper and sesquisulphuret of 

 iron, or a sulphur salt, Cu 2 S + Fe 2 S 3 , but in which the two 

 sulphurets are also found in other proportions, and which often 

 contains an admixture of the bisulphuret of iron. Few metal- 

 lurgic processes require more skill and attention than the 

 extraction of copper from this ore. The first object of the 

 process is, by roasting the ore at a high temperature, in contact 

 with siliceous matter, to oxidate and convert the iron into 

 a fusible silicate or slag, while the less oxidable copper is ob- 

 tained as the fusible subsulphuret of copper, but still contami- 

 nated with a considerable quantity of protosulphuret of iron. 

 By alternate oxidation of the last product, and reduction by 

 carbonaceous matter in contact with quartzy sand, more of the 

 iron and other oxidable substances are separated in the form of 

 scoriae, and the same end is afterwards more perfectly attained 

 by directing a strong blast of air upon the surface of the melted 

 copper. 



