60 PTROMETALLTJRaY. [III. 



then thrown down bj iron, the precipitate calcined to oxidize 

 the copper, which is to be dissolved out with muriatic or sul- 

 phuric acid. 



A better method for pyritous ores is to roast them partially, 

 if not already oxidized, and to melt them in a low blast-furnace, 

 using a siliceous ore as a flux, if necessary. A large portion 

 of oxide of iron will thus be removed, and the gold concen- 

 trated in the remaining sulphuret of iron, which could then 

 be worked by dilute sulphuric acid. — '/. 0. B. 



On the use of chloride of lime and hyposulphites, for ex- 

 tracting gold from its ores, see an essay by Percy, in Phil. 

 Mag. 3 ser. xxxvi. 1-8. 



Tougliening Gfold. — "Wolff proposes, in the Practical Hand- 

 book for Jewellers, to fuse the brittle gold in a new crucible, 

 and when melted to throw in one or two pieces of sulphur of 

 the size of a pea, to shake the crucible a little with the tongs, 

 and to cast it rapidly into a heated mould. He also proposes to 

 render small pieces malleable by coating them with powdered 

 borax, and heating them in the blowpipe flame until the surface 

 commences fusion. 



Both of these methods are resorted to at the United States 

 Mint, but the choice of either depends upon the nature of the 

 accompanying metals that give the gold its brittle character. 

 When there is a quantity of iron present, the gold is fused 

 with a mixture of sulphur, potash, and soda, which will remove 

 it by making the very fusible mixture of sulphurets of iron 

 and alkali. If tin, arsenic or antimony be present, a good 

 flux is a mixture of borax, soda, and saltpeter, the last for 

 oxidizing the foreign metals into their respective acids, the 

 soda to give base to those acids, and the borax to collect the 

 slag. In both these cases, a sand or clay crucible is preferable 

 to a black-lead pot, in which last the graphite acts reducingly. 

 "Where lead is present, this process may partially effect its 

 removal ; but it is more completely effected during quartation 

 and by washing the fine gold thoroughly with hot water, after 

 extracting the silver by nitric acid. Another method of re- 

 moving lead would be to fuse the gold with a little saltpeter, 



