The Eatraction of Cold. 19 
left in the tailings will depend on whether it has been 
deposited in the quartz in fine or coarse particles, and 
also on the more or less perfect character of the means 
used for retaining it. A small per centage also is left 
in the waste consisting of gold still attached to particles of 
quartz. 
The plan first adopted by our miners was to roast the 
quartz in stacks in the open air, or in kilns, to oxidise the 
sulphides, and so liberate the gold, while the quartz was 
rendered more friable and easy to crush. After several years’ 
trial this system was given up, as it was found to be rather 
injurious than otherwise. Ata low heat the pyrites in the 
interior of the quartz was little changed, while the free gold 
was coated with a film of some material, probably sulphur, 
which impeded the action of the mercury on it. When the 
roasting was carried on with a higher degree of heat, the 
oxide of iron formed on the exposed faces of the quartz acted 
as a flux, and a glazed surface of slag wa formed, in which 
numerous minute globules of gold could be discerned under 
the microscope, similar to those found in the waste tailings 
when crushing roasted quartz. In the interior of the quartz 
only a portion of the sulphur was given off, while black veins 
were formed by the melted mono-sulphide of iron ; and other 
experiments led to the conclusion that a portion of the melted 
gold was diffused through these black veins ina form which 
rendered it more difficult to separate than when in its natural 
state. A careful experiment made on quartz roasted ina 
cupola furnace with a superabundance of heated air, showéd 
that the loss of gold sustained in crushing was ten per cent. 
more than it would have been if the same quartz had been 
crushed raw. Even if the pyritous gold could have been 
liberated previous to crushing the quartz, it isin such a 
minute state of division that much of it would have been 
lost in the treatment found to be the most economical for 
extracting the free gold. 
These experiments indicated that the attempt to liberate 
the pyritous gold by roasting the quartz before it was 
crushed only increased the loss, and that attention should be 
directed to the separation of this pyritous gold from the 
sand after the latter had passed the different processes used 
for retaining the free gold. The plan it was first proposed 
to carry out was to operate on the waste tailings in bulk, 
and as this is the principle on which the attempt at improve- 
ments are based in California and other mining countries, it 
C 2 
