EXTRACTION OF GOLD FROM ORES. 59 



B. 



Gold.... 

 Silver .. 

 Copper. 



Iron 



Silica . . 



100.0 99.73 99.88 



California gold has a dark color, from its light coating of 

 oxide of iron ; but "when fused, its light color indicates a large 

 percentage of silver. The average fineness of California gold, 

 as determined by some thousand assays at the United States 

 Mint, Philadelphia, is 885 thousandths, or 88| per cent, pure 

 gold, and 115th or llj per cent, silver, omitting mere traces 

 of other metals. For Iridosmin, see below. 



The gold production of Russia in 1847 was about 17f mil- 

 lions of dollars, and supposing it to have increased 100 pounds 

 per annum, it would amount to 20 millions in 1850. The pro- 

 duce of California may be estimated at 50 millions. These 

 numbers being moderate estimates from known returns, the 

 quantity of gold from the new sources of this metal in Russia 

 and the United States was 70 millions, or more than 300,000 

 troy pounds, in 1850. 



Extraction of Gold from Ores. — Allain and Bartenbach's 

 process (Comptes Rendus, 1849) for extracting gold is ap- 

 plicable to all pyritous ores, even when the proportion of noble 

 metal does not exceed two ten-thousandths. For working ore 

 containing this quantity, the expense will be about $40 for 

 every pound of gold obtained. 



The ore, after being roasted in the air, is powdered, sieved, 

 re-roasted into a red mass, made into paste with sulphuric 

 acid of 66°, and again roasted until the entire cessation of 

 sulphurous fumes. Sulphur, zinc, and copper are thus largely 

 removed. The ore is now reduced to a still finer powder, 

 boiled with dilute oil of vitriol, and the undissolved residue 

 digested in a mixture of 6 pts. muriatic acid of 21° and 1 pt. 

 nitric acid of 36°, diluted with water. Copper and gold are 



