y dissolved from their salts and held in solution in the same
mineral water, they would in many cases not be deposited together, for
the reason that silver is most readily deposited in the presence of
alkalies, which would be found in excess in mineral waters coming direct
from the basic rocks, while gold is induced to precipitate more quickly
in acid solutions, which would be the character of the waters after
they had been exposed to atmospheric action and to contact with organic
matters.

This, then, may explain not only the comparatively greater purity of the
alluvial gold, but also why big nuggets are found so far from auriferous
reefs, and also why heavy masses of gold have been frequently unearthed
from among the roots even of living trees, but more particularly in
drifts containing organic matter, such as ancient timber.

All, then, that has been adduced goes to establish the belief that the
birthplace of our gold is in certain of the earlier rocks comprising the
earth's crust, and that its appearance as the metal we value so highly
is the result of electro-chemical action, such as we can demonstrate in
the laboratory.

CHAPTER VI

GOLD EXTRACTION

We now come to a highly important part of our subject, the practical
treatment of ores and matrixes for the extraction of the metals
contained. The methods employed are multitudinous, but may be divided
into four classes, namely, washing, amalgamating with mercury,
chlorinating, cyaniding and other leaching processes, and smelting. The
first is used in alluvial gold and tin workings and in preparing some
silver, copper, and other ores for smelting, and consists merely in
separating the heavier metals and minerals from their gangues by their
greater specific gravity in water. The second includes the trituration
of the gangue and the extraction of its gold or silver by means of
mercury. Chlorinating and leaching generally is a process whereby
metals are first changed by chemical action into their mineral salts,
as chloride of gold, nitrate of silver, sulphate of copper, and being
dissolved in water are afterwards redeposited in the metallic form by
means of well-known re-agents.

In really successful mining it is in the last degree important that the
mode of extraction of metals in the most scientific manner should be
thoroughly understood, but as a general rule the science of metallurgy
is but very superficially grasped even by those whose special business
i