rge saving of cyanide of potassium by regeneration; not wasting
the solutions, larger recovery of the gold and silver from the
solutions; the cost of recovery less; the loss of gold, silver, and
cyanide of potassium reduced to a minimum; the use of caustic alkali in
such quantity as may be desired to keep the cyanide solution from
being destroyed by the solidity of the pulp, and also sometimes to give
warmth, as a warm cyanide solution will dissolve gold and silver quicker
than a cold one. These caustic alkalies do not interfere with or prevent
the perfect precipitation of the metals. The bullion recovered in this
process is very fine, while the zinc-precipitated bullion is only about
700 fine.

"The gold and silver is dissolved, and then precipitated in one
operation, which we know cannot be done in the 'chlorination
process'; besides, the cost of plant and treatment is much less in the
above-described process.

"The electro-chemical process, which I have hastily sketched will, I
think, be the future cheap method of recovering fine or flour gold from
our mines and waste tailings or ore dumps.

"Without going into details of cost of treatment, I will state that with
a plant of a capacity of handling 10,000 tons of pulp per month,
the cost should not exceed 8s. per ton, but that may be cheapened by
labour-saving devices. There being no expensive machinery, a plant could
be very cheaply erected wherever necessary."

CHAPTER VIII

CALCINATION OR ROASTING OF ORES

The object of calcining or roasting certain ores before treatment is
to dissipate the sulphur or sulphides of arsenic, antimony, lead,
etc., which are inimical to treatment, whether by ordinary mercuric
amalgamation or lixiviation. The effect of the roasting is first to
sublimate and drive off as fumes the sulphur and a proportion of the
objectionable metals. What is left is either iron oxide, "gossan," or
the oxides of the other metals. Even lead can thus be oxidised, but
requires more care as it melts nearly as readily as antimony and is
much less volatile. The oxides in the thoroughly roasted ore will not
amalgamate with mercury, and are not acted on by chlorine or cyanogen.

To effect the oxidation of sulphur, it is necessary not only to bring
every particle of sulphur into contact with the oxygen of the air, but
also to provide adequate heat to the particles sufficient to raise them
to the temperature that will induce oxidation. No appreciable eff