ch varies therefore from 3 to 15 lb. to the square inch.
The quantity of air consumed in a converter which will blow up about 35
tons of matte per day is about 3000 cub. ft. per minute. The operation
of raising a charge of 50% matte to copper usually consists of two
blows. The first blow occupies about 25 minutes, and oxidizes all but a
small quantity of the iron and some of the sulphur, raising the product
to white metal. The slag is then poured and skimmed, the blast turned on
and converter retilted. During the second blow the sulphur is rapidly
oxidized, and the charge reduced to metal of 99% in from 30 to 40
minutes. Little or no slag results from the second blow. That from the
first blow contains between 1% and 2% of copper, and is usually poured
from ladles operated by an electric crane into a reverberatory, or into
the settling well of the cupola. The matte also, in all economically
planned works, is conveyed, still molten, by electric cranes from the
furnace to the converters. When lead or zinc is not present in notable
quantity, the loss of the precious metals by volatilization is slight,
but more than 5% of these metals in the matte is prohibitive. Under
favourable conditions in the larger works of the United States the cost
of converting a 50% matte to metallic copper is generally understood to
be only about 5/10 to 6/10 of a cent per lb.. of refined copper.

_Pyritic Smelting._--The heat generated by the oxidation of iron and
sulphur has always been used to maintain combustion in the kilns or
stalls for roasting pyrites. Pyritic smelting is a development of the
Russian engineer Semenikov's treatment (proposed in 1866) of copper
matte in a Bessemer converter. Since John Hollway's and other early
experiments of Lawrence Austin and Robert Sticht, no serious attempts
have been made to utilize the heat escaping from a converting vessel in
smelting ore and matte either in the same apparatus or in a separate
furnace. But considerable progress has been made in smelting highly
sulphuretted ores by the heat of their own oxidizable constituents. At
Tilt Cove, Newfoundland, the Cape Copper Company smelted copper ore,
with just the proper proportion of sulphur, iron and silica,
successfully without any fuel, when once the initial charge had been
fused with coke. The furnaces used were of ordinary design and built of
brick. Lump ore alone was fed, and the resulting matte showed a
concentration of only 3 into 1. When, howev