ted to be a cheaper mode of
lixiviation by chlorine. It is the invention of Mr. J. H. Pollok, of
Glasgow University, and a strong Company was formed to work it. With him
the gas is produced by the admixture of bisulphate of sodium (instead
of sulphuric acid, which is a very costly chemical to transport)
and chloride of lime. Water is then pumped into a strong receptacle
containing the material for treatment and powerful hydraulic pressure is
applied. The effect is stated to be the rapid change of the metal into
its salt, which is dissolved in the water and afterwards treated with
sulphate of iron, and so made to resume its metallic form.

It appears, however, to me that there is no essential difference in the
pressure brought to bear for the quickening of the process. In each case
it is an air cushion, induced in the one process by the pumping in of
air to a cylinder partly filled with water, and in the other by pumping
in water to a cylinder partly filled with air.

The process of extracting gold from lode stuff and tailings by means
of cyanide of potassium is now largely used and may be thus briefly
described:--It is chiefly applied to tailings, that is, crushed ore
that has already passed over the amalgamating and blanket tables. The
tailings are placed in vats, and subjected to the action of solutions
of cyanide of potassium of varying strengths down to 0.2 per cent. These
dissolve the gold, which is leached from the tailings, passed through
boxes in which it is precipitated either by means of zinc shavings,
electricity, or to the precipitant. The solution is made up to its
former strength and passed again through fresh tailings. When the
tailings contain a quantity of decomposed pyrites, partly oxidised, the
acidity caused by the freed sulphuric acid requires to be neutralised by
an alkali, caustic soda being usually employed.

When "cleaning up," the cyanide solution in the zinc precipitating boxes
is replaced by clean water. After careful washing in the box, to cause
all pure gold and zinc to fall to the bottom, the zinc shavings are
taken out. The precipitates are then collected, and after calcination in
a special furnace for the purpose of oxidising the zinc, are smelted in
the usual manner.

The following description of an electrolytic method of gold deposition
from a cyanide solution was given by Mr. A. L. Eltonhead before the
Engineers' Club of Philadelphia.

A description of the process is as follows:-