RECEIPT COPPEE-EXTEACTING PROCESSES. 137 



where tlie heap of debris already crushed will exist — where it 

 shall consist of carbonates and oxides — where iron pyrites is 

 found in abundance for the manufacture of sulphuric acid, &e. ; 

 but we can find many places where a little modification of the 

 process may be made with profitable results — where large deposits 

 of copper pyrites exist, containing 2 to 3 per cent, of copper, the 

 pyrites itself serving in many cases for providing its own sul- 

 phuric acid, for the subsequent treatment of the oxidized or 

 desulphurized ore. 



The Sitowden, or Lime Process, 

 is' the next deserving of mention, on account of its simplicity and 

 easy application in places difficult of access in the far interior, 

 where the usual requirements of a reduction establishment and 

 skilled labour would be difficult to obtain, and even valueless for 

 the poor class of ores that may be treated by the process. 



There are two necessary conditions to its application : 1st. 

 That the ores, or a considerable portion of them, shall be sul- 

 phurets ; and 2nd, that limestone be obtainable on the ground. 



The process is as follows : — The mineral, containing copper 

 pyrites is crushed, mixed with a small proportion (rarely exceed- 

 ing 5 per cent.) of burnt lime ; the lime and pyrites are then 

 moistened and shaped by machinery into bricks, stacked, and 

 roasted at a low red heat for a short time. The lime and pyrites 

 undergo a double decomposition, the sulphide of copper being 

 converted into a sulphate, and the lime into a sulphide of calcium. 

 The bricks are then rapidly passed through a crusher into water, 

 where the soluble sulphate of copper is at once removed ; suc- 

 cessive lots are passed into the same liquor, which becomes 

 strongly acid ; and if any oxide should have been present 

 originally in the ore, or be formed by careless roasting, it will be 

 dissolved out in the strongly acid liquor. After being allowed to 

 settle, it is drawn off into another tank, and the copper is 

 .precipitated by passing hydrogen sulphide through the solution. 

 The resulting product will contain 50 per cent of copper. The 

 entire cost of treatment, inclusive of 10s. per ton for mining the 

 ore, is about 20s. per ton, so that an ore of two per cent, could be 

 worked at a very good profit, if the ore is plentiful and readily 

 procured. The hydrogen sulphide is made from the ores them- 

 selves. Very little apparatus is wanted for conducting the pro- 

 cess ; a good bush carpenter could make the tanks of hardwood, 

 taking care to use no metal in any part, at least inside, or at the 

 joints ; the bricks can be made by hand ; the furnace for gene- 

 rating the hydrogen sulphide could be put up in a few days by 

 an ordinary bricklayer working from a plan. The crushing of the 

 ore will require some appliance, unless in the first instance it is 

 reduced by a dolly, shod with iron, worked by a long lever, an 

 appliance by which a few hundredweights can soon be reduced 



