22 The Extraction of Gold. 
fire, hollow fire-bars, communicating with a hollow bridge, 
and, if. necessary with a coil of air-pipes in the ash-pit; the 
object being to supply a large amount of oxygen in the 
heated air to combine with the sulphur and arsenic, forming 
sulphurous and arsenious acids, which pass off in a gaseous 
state, thus converting the sulphides into oxides having no 
deteriorating action on the mercury, and capable of ready 
disintegration to allow of the liberation of the gold. The 
sand is spread over the bed of the furnace ina thin layer, 
and requires about two hours’ exposure to be roasted per- 
fectly at a dull red heat. Soon as it comes out of the furnace 
the heated sand is quenched with water, and when cool it 1s 
ground and amalgamated in a damp state in Chilian mills, a 
very good system, first introduced into this colony by Mr. 
Hinck. About 2 ewt. of roasted sand is placed in the mill 
for a charge with half its weight of mercury. This is ground 
for half-an-hour, the mercury breaking up and becoming dis- 
tributed through the sand in small globules. When itis 
supposed the mercury has had time to absorb the gold, water 
is admitted, and the globules collect together again. The 
sand is then flushed out and another charge placed in the 
mill. Some of the broken mercury escapes with the sand, 
and provision must be made for its separation from the waste 
before the latter finally passes away. 
The following return gives the results obtained at the 
Clunes works for the first six months of the current year in 
operating on the pyritous sand saved from the waste in the 
way described before :— 
Quantity of concentrated sand treated - 
Amount of gold obtained’ - it “ . 
Cost of concentrating and reducing -  - 
183 tons 
539 ozs. 17 dwts. . 
£560 
3) 
Profit on the six months’ work - - £1,422 5s. 8d. 
- Proportion of the total gold contents obtained 87 per cent. 
Loss of mercury per ton of sand treated - 2°8 lbs. 
The loss of mercury was heaviest at the beginning of the 
year ; in the last parcel treated it was reduced to 1-6 Ibs. per 
ton. Changes are now in contemplation intended to decrease 
this loss still more, and at the same time increase the per 
centage of gold obtained. But even in its present state this 
is a good practical system of treating the sulphides, giving 
fair returns both as regards the profit and the proportion of 
gold extracted; and it should be noted that this is not a 
mere laboratory experiment, but the results obtained in 
actual working on a large scale, under conditions where 
each step of the process is accurately tested. - 
