er 75 lb. at intervals
during the middle of the process, and finally another lot of 75 lb.
shortly before the termination. When treating "pacos," or earthy chlorides
of silver, assaying only 20 oz. to 30 oz. of silver to the ton, 36 lb. of
mercury is added to 21/2 tons of ore at three different stages of the
process as just described.

The _rationale_ of the process therefore appears to be that the
chlorination of the ores is only partially effected during the roasting,
so as to prevent the formation of injurious salts, and is completed in the
vats, in which the chloride of copper is formed progressively as required,
by the gradual grinding away of the copper by friction between the bottom
copper plates and the stirrer; and this chloride subsequently becoming
incorporated with the boiling brine is considered to quicken the action of
the mercury upon the silver.

_Subliming_.--The subliming furnace, shown in Figs. 5 and 6, is a plain
cylindrical chamber, A, about 4 ft. diameter inside and 41/2 ft. high, lined
with firebrick, in the center of which is fixed the upright cast-iron
cylinder or retort, C, of 1 ft. diameter, closed at top and open at
bottom. The furnace top is closed by a cast-iron lid, which is lifted off
for charging the fuel. Round the top of the furnace is a tier of radial
outlet holes for the fuel smoke to escape through; and round the bottom is
a corresponding tier of inlet air-holes, through which the fuel is
continually rabbled with poles by hand. The fuel used is llama dung,
costing 80 cents, or 2s. 6d., per 250 lb.; it makes a very excellent fuel
for smelting purposes, smouldering and maintaining steadily the low heat
required for subliming the mercury from the amalgam. Beneath the furnace
is a vault containing a wrought-iron water-tank, B, into which the open
mouth of the retort, C, projects downward and is submerged below the
water. For charging the retort, the water-tank is placed on a trolly; and
standing upright on a stool inside the tank is placed the pina, or conical
mass of silver amalgam, which is held together by being built up on a
core-bar fitted with a series of horizontal disks. The trolly is then run
into the vault, and the water-tank containing the pina is lifted by
screw-jacks, so as to raise the pina into the retort, in which position
the tank is then supported by a cross-beam. The sublimed mercury is
condensed and collected in the water; and on the completion of the process
the ta