Moreover, the working of the dry method has been
monopolised by a small ring of assayers, with the double result of
exciting outside jealousy and, worse still, of retarding the development
and improvement of the process.
The principal stages of the dry assay are: (1) the concentration of the
copper in a regulus; (2) the separation of the sulphur by calcining; (3)
the reduction of the copper by fusion; and (4) the refining of the metal
obtained.
The whole of these operations are not necessary with all copper
material. Ores are worked through all the stages; with mattes, the
preliminary fusion for regulus is omitted; precipitates are simply fused
for coarse copper, and refined; and blister or bar coppers are refined,
or, if very pure, subjected merely to washing.
The quantity of ore generally taken is 400 grains, and is known as "a
full trial"; but for rich material, containing more than 50 per cent. of
copper, "a half trial," or 200 grains, is used.
~Fusion for Regulus.~--The ore (either with or without a previous
imperfect roasting to get rid of any excess of sulphur) is mixed with
borax, glass, lime, and fluor spar; and, in some cases, with nitre, or
iron pyrites, according to the quality of the ore. The mixture is placed
in a large Cornish crucible, and heated as uniformly as possible in the
wind furnace, gradually raising the temperature so as to melt down the
charge in from 15 to 20 minutes.
Pages:
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341