THE SOURCES AND USES OF IRON PYRITES. 
123 
The silver contained in these ores was for some time lost, but 
by a process invented by Mr. Claudet, it is now, to a very large 
extent, recovered, and a portion of the gold is at the same time 
obtained. 
Nearly the whole of the precious metals present in the burnt 
ores is contained in the first three washings from the roasted 
cinder, and, after ascertaining, by means of an assay, the propor- 
tion of silver present, a sufficient amount of a standardised solu- 
tion of iodide of potassium is added. This causes the precipi- 
tation of the silver in the form of an insoluble iodide of that 
metal. The whole is then allowed to stand for forty- eight hours, 
in order to allow the precipitate to settle, and the supernatant 
copper liquor is afterwards run off to the tanks containing iron 
for precipitation. 
The argentiferous precipitate, after having been duly washed, 
is decomposed by boiling with metallic zinc ; by this treatment, 
on the one hand, a mixture of metallic silver with sundry im- 
purities and a notable amount of gold is obtained, while on the 
other a solution of iodide of zinc is produced, which is stan- 
dardised and employed in subsequent operations. In this way 
the valuable substance iodine is used over several times with 
only a slight loss upon each operation. During the year 1877, 
124,500oz. of silver, and 320oz. of gold were recovered by 
Claudet’s process from liquors resulting from the treatment of 
Spanish and Portuguese pyrites. 
The chief production of Spanish and Portuguese pyrites is 
from the mines of Tharsis, Rio Tinto, and San Domingos, but 
small quantities of this mineral are likewise obtained from 
sundry other localities. Of the total annual export from these 
countries about 600,000 tons, representing 280,000 tons of 
sulphur, are consumed in this country. In addition to this 
54,000 tons of sulphur in the form of brimstone were imported 
in 1877 ; thus bringing the grand total of our consumption for 
that year up to 334,000 tons. A portion of the sulphur im- 
ported in the form of brimstone is employed for the preparation 
of gunpowder and for various other purposes, but a large pro- 
portion of it, as well as nearly the whole of that existing in the 
form of pyrites, is consumed either by alkali makers or by arti- 
ficial manure manufacturers. 
The amount of common salt decomposed by sulphuric acid 
during the year 1877 was 578,201 tons, while from the resulting 
sulphate of soda were prepared 223,776 tons of dry carbonate of 
soda, 169,769 tons of crystallised carbonate of soda, 74,663 tons 
of caustic soda, and 12,109 tons of bicarbonate of soda. In ad- 
dition to this 105,529 tons of bleaching powder were prepared 
from hydrochloric acid resulting from the action of oil of vitriol 
upon common salt. 
