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760- IX. mining industry and metal production op sweden.
For determining the percentage of gold in iron and copper pyrites as well
as in silicic ores, Planner’s tests are used. After the ore has been crushed fine
and perfectly roasted, 300 grams are weighed up, and in a somewhat damp
condition this ore is subjected to the effects of chloride gas, after which the
chloride of gold formed is extracted by means of an aqueous chloric solution. The
surplus of chloride is expelled by means of evaporation, and the gold is
precipitated with ferro sulphate, collected on a filter, and expelled, after its combustion,
together with some silver and lead on a cupel of bone-ashes, after which the
silver is liberated by boiling with nitric acid, and the remaining gold is weighed.
— For determining the percentage of gold occurring in copper, regains, etc., they
are dissolved in nitric acid, and the remaining gold is treated as aforesaid.
Silver. Production of silver and lead now only takes place at Sola
and Kafveltorp, where silverbearing galena is worked, and at the
copper-extraction works at Falun, Åtvidaberg, and Helsingborg, where silvers
procured as a by-product by precipitating from copper-solutions.
Among the aforesaid silver-works, Sala takes the foremost place. Its
existence goes back as far as to the close of the fifteenth century, but it cannot be
definitely determined how much earlier silver production took place there. The
State has for many centuries supported these works by privileges consisting in
grants of land and forests and in the right to get charcoal from adjacent parishes.
On the other hand, the State had the right to conduct the works through the
Board of Mines, and to hold for its own account ’/io of the silver produced. This
state of things continued till the close of 1890, when the mine and the works
were bought by a private company.
The production in Sala, which at the time of Gustavus Vasa (1523/60) amounted
on the average to 3,000 kilogram annually, has of låte decreased so that during the
last decades it has only amounted to 2,000 kilogr. of silver and 1,500 tons of lead.
Since the new company took over the mine, the production has again at certain
times increased by the purchase of ore from other mines and by improved methods
for enriching and melting the ore. Still the production amounted in 1902 only
to 990 tons of marketable lead, and 957 kilogr. of silver.
The silver-percentage in the pure galena varies considerably in different
parts of the mine and in different samples, namely from 1*5 to O-ss The
percentage has not been found to depend in any way upon the structure of the
galena, such as being more or less granulated. On an average, the
silver-percentage is such that the lead obtained contains 0*8 o % of silver.
The silver-percentage of the ore, slag, etc., is determined either by the so-called
»boiling» process, or by melting with carbonate of soda in iron melting crucibles. In
making the »boiling» test — which is principally used for slags and alloys,
especially when they contain copper and arsenic — 3 grams of the pulverized substance
are mixed with granulated lead and melted together with borax in muffles in a
so-called essayer of fire-proof clay, when some lead, together with foreign substances,
becomes slag and is absorbed by the melted borax. When so much slag has been
obtained that it covers the lead, and no further oxidizing takes place, the lead is
poured into a chill and afterwards driven off on a cupel of bone-ashes.
Lead is not produced otherwise than in connection with silver, and
only at Sala and Kafveltorp. Concerning the amount of the production, see
Table 110,page 754. The world’s total production during 1896/1900 amounted
to 794,000 tons per annum; Sweden’s contribution amounted to 1,520 tons, or
only 0-2 %. In 1902 the Swedish production had decreased to 843 tons.
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