THE MONNIER PR CESS OF BED V CIN G^ ORES. 331 



An intensely heated draft of air passes steadily from the fire-box (7) into 

 the lower end of the cylinder. The mixture is thus heated to a high degree, 

 until at the lower end (b) the ore reaches a dark red heat. This roasting 

 within the cylinder gradually transforms the sulphurets^into sulphates and 

 the gold is set free. Chemically this is explained by the^sulphur becoming 

 oxidized and forming sulphuric acid. This combines with the soda, form- 

 ing a bisulphate of soda, the decomposition of which reduces successfully the 

 sulphurets of iron, etc. A considerable quantity of sulphurous acid is also 

 formed and escapes from the cylinder. The resulting sulphates being solu- 

 "ble in water, you can look with safety from the upper end of the cylinder 

 through its entire length, and see myriads of brilliant scintillations flying to 

 and fro, and falling like so many meteors in miniature. These are caused 

 hy the union of sulphur with the oxygen from the atmospheric air. The 

 •degree of heat required is maintained by consuming in the fire-box half a 

 •cord of mountain cedar each 24 hours. The red hot ore passes at b into an 

 iron wheelbarrow, which is trundled by one man along tramway {t), passing 

 over five huge wooden tanks (8), made on the Monnier plan, and^partly filled 

 with water at its natural temperature. Here the process of lixiviation be- 

 gins. The: man wko handles the wheelbarrow takes the roasted ore from it 

 by the shovelful and di^ops it into any one of the lixiviating tanks. Quite a 

 detonation follows as each shovelful is thrown in. This is continued until 

 each tank receives its allowance. 



By a set of rubber tubes connection is kept up between the liquid in three 

 of the tanks at a time, thus forming a battery. 



When the water in any of the five tanks holds in solution the largest pos- 

 sible amounts of sulphates of silver, copper and soda, it is sent by a tube into 

 small tanks filled with cement copper by which the silver is precipitated. 

 Thence the remaining liquid is run into a reservoir (10). This is done in 

 whiit is called the silver room. 



Any weaker solution is passed into another reservoir (10), to be used 

 again in lixiviating till it attains sufficient strength 



From the reservoir (10) the solution is conducted by a wooden pump and 

 trough into a tank under tank 11. Thence it is raised by a wooden pump 

 into the latter tank, which serves as a feeder (11) for the evaporator. This 

 huge evaporator is filled through a wooden trough from tank 11, and the 

 liquid in it is kept at boiling heat by the hot air passed into it from the 

 revolving cylinder and the fire-box. 



After a certain time allowed for evaporation the remaining liquid is pas- 

 sed by rubber syphons from the evaporator into the crystallizing tank (13). 

 This ta^ik now contains only sulphates of copper and soda in solution. As 

 the liquid cools, the sulphate of soda crystallizes, and is drawn out by an iron 

 hoe with a long handle into a pile (^2), to be used over again to repeat the 

 process ad infinitum. The amount lost is scarcely appreciable. 



The copper in solution is then precipitated by iron. All the round tanks 

 are about the same size, having a capacity of some 700 cubic feet. The five 



