._--As soon as
the pneumatic method of decarburizing pig iron was accepted as
practicable, experiments were made with a view to Bessemerizing copper
ores and mattes. One of the earliest and most exhaustive series of
experiments was made on Rio Tinto ores at the John Brown works by John
Hollway, with the aim of both smelting the ore and concentrating the
matte in the same furnace, by the heat evolved through the oxidation of
their sulphur and iron. Experiments along the same lines were made by
Francis Bawden at Rio Tinto and Claude Vautin in Australia. The
difficulty of effecting this double object in one operation was so great
that in subsequent experiments the aim was merely to concentrate the
matte to metallic copper in converters of the Bessemer type. The
concentration was effected without any embarrassment till metallic
copper commenced to separate and chill in the bottom tuyeres. To meet
this obstacle P. Manhes proposed elevated side tuyeres, which could be
kept clear by punching through gates in a wind box. His invention was
adopted by the Vivians, at the Eguilles works near Sargues, Vaucluse,
France, and at Leghorn in Italy. But the greatest expansion of this
method has been in the United States, where more than 400,000,000 lb.
of copper are annually made in Bessemer converters. Vessels of several
designs are used--some modelled exactly after steel converters, others
barrel-shaped, but all with side tuyeres elevated about 10 in. above the
level of the bottom lining. Practice, however, in treating copper matte
differs essentially from the treatment of pig iron, inasmuch as from 20
to 30% of iron must be eliminated as slag and an equivalent quantity of
silica must be supplied. The only practical mode of doing this, as yet
devised, is by lining the converter with a silicious mixture. This is so
rapidly consumed that the converters must be cooled and partially
relined after 3 to 6 charges, dependent on the iron contents of the
matte. When available, a silicious rock containing copper or the
precious metals is of course preferred to barren lining. The material
for lining, and the frequent replacement thereof, constitute the
principal expense of the method. The other items of cost are _labour_,
the quantity of which depends on the mechanical appliances provided for
handling the converter shells and inserting the lining; and the _blast_,
which in barrel-shaped converters is low and in vertical converters is
high, and whi