surface. They must next provide a reducing plant. Of means for crushing
or triturating quartz there is no lack, and every year gives us fresh
inventions for the purpose, each one better than that which preceded
it, according to its inventor. Most practical men, however, prefer to
continue the use of the stamper battery, which is virtually a pestle
and mortar on a large scale. Why we adhere to this form of pulverising
machine is that, though somewhat wasteful of power, it is easily
understood, its wearing parts are cheaply and expeditiously replaced,
and it is so strong that even the most perversely stupid workman cannot
easily break it or put it out of order.

The stone, being pounded into sand of such degree of fineness as
the gold requires, passes through a perforated iron plate called a
"grating," or "screen," on to an inclined surface of copper plates faced
with mercury, having small troughs, or "riffles," containing mercury,
placed at certain distances apart.

The crushed quartz is carried over these copper "tables," as they are
termed, thence over the blanket tables--that is, inclined planes covered
with coarse serge, blankets, or other flocculent material--so that the
heavy particles may be caught in the hairs, or is passed over vanners or
concentrating machines. The resulting "concentrates" are washed off from
time to time and reserved for secondary treatment.

To begin with, they are roasted to get rid of the sulphur, arsenic,
etc., which would interfere with the amalgamation or lixiviation, and
then either ground to impalpable fineness in one of the many triturating
pans with mercury, or treated by chlorine or potassium cyanide.

If, however, we are merely amalgamating, then at stated periods the
battery and pans are cleaned out, the amalgam rubbed or scraped from
the copper plates and raised from the troughs and riffles. It is then
squeezed through chamois leather, or good calico will do as well, and
retorted in a large iron retort, the nozzle of which is kept in water so
as to convert the mercury vapour again to the metallic form. The result
is a spongy cake of gold, which is either sold as "retorted" gold or
smelted into bars.

The other and more scientific methods of extracting the precious metal
from its matrices, such as lixiviation or leaching, by means of solvents
(chlorine, cyanogen, hyposulphite of soda, etc.), will be more fully
described later on.

CHAPTER II

GOLD PROSPECTING--ALLUVIA