122 
POPULAR SCIENCE REVIEW. 
Sulphur 49*00 
Arsenic ...... *47 
Iron 43*55 
Copper 3*20 
Zinc *35 
Cobalt trace 
Silver trace 
Lead *93 
Lime *10 
Insoluble residue ..... *63 
Water *70 
Oxygen and loss 1*07 
idado 
When this ore is burnt for the production of sulphuric acid,, 
the resulting cinder may he taken to have, approximately, the 
following composition : — 
Sulphur 
Arsenic 
Iron . 
Copper 
Zinc . 
Cobalt 
Silver 
Lead . 
Lime . 
Insoluble residue 
Water 
Oxygen and loss 
10(H)0 
•25 
58*25 = 83 °| o Fe 2 0 s 
4*14 
*37 
trace 
trace 
1*14 
*25 
1*06 
3*85 
26*93 
The amount of silver in burnt ore varies from 15 or 18 dwt„ 
per ton in the San Domingos cinders, to loz. 15dwt. in that 
from Rio Tinto pyrites. A few grains of gold per ton are also 
contained in all Spanish and Portuguese ores. 
In order to obtain the copper by the wet process of extraction, 
the burnt ore is first finely ground and sifted, and subsequently 
roasted with about 12 per cent, of common salt until, by the 
oxidation of the metallic sulphides, a portion of the salt is con- 
verted into sulphate of soda, while the copper becomes trans- 
formed into a soluble chloride. The copper salt is subsequently 
removed by repeated washings with hot water, and the copper 
precipitated in the metallic state by scrap iron. 
After the removal of the copper by solution the residual 
“ purple ore” or “blue billy” is thrown out of the washing vats,., 
which are again filled with freshly roasted ore, and the operation 
proceeds as before. The purple ore so obtained contains 96 per 
cent, of peroxide of iron, equal to 67 per cent, of metallic iron, 
and as it contains no phosphorus, and only traces of sulphur, it 
is largely employed in the blast-furnace as a source of iron, as* 
well as for the lining of puddling furnaces. 
