1865.] MACFARLANE — EXTRACTION OF COPPER. 231 



the following mixture containing only one fifth part of salt was 

 calcined : 



2000 grains residue of 1*1 per cent = 22 grains copper. 



1000 " fresll ore of 8-6 " =86 " 

 200 " salt 



3200 grains containing 108 grains copper. 



This experiment was made with the same care as the others, 

 and with as little stirring as possible. The result weighed 3250 

 grains, and contained 



2-33 per cent, soluble in water = 76-7 grains copper. 



•44 " " in dilute acid = 14-3 " 



Unaccounted for = 17*0 " 



108-0 



Since therefore only 71 per cent of the copper was extracted, it 

 follows that one fourth of salt is the minimum quantity which can 

 be used, and at the same time a complete extraction accomplished. 



I here closed this series of experiments, having obtained all the 

 definite results sought for. It appears certain that 95 per cent of 

 the copper contained in an ore such as that produced by the Capel 

 mine can be extracted in the humid way by calcining it with 

 twice its weight of impure iron oxide (perhaps less would be suffi- 

 cient), and one fourth of its weight of salt ; provided always that the 

 operation is performed at a very low temperature, that it is not 

 continued beyond a certain point, and that while it is going on the 

 materials are stirred as little as possible. Whether equally good 

 results can be obtained in practically applying this process, is a 

 matter which can only be decided by experience ; but there ap- 

 pears to be no reason for doubting that it would be completely 

 successful on the large scale. 



