TIN MINING IN PERAK. 33 



zinc box. The ore, altered in no respect except that the gold 

 has been extracted from it, could then be dried and bagged 

 for the local smelting furnaces or for export. 



This process seemed so promising that a trial of it was 

 undertaken by the writer. Ten pikuls of the auriferous tin - ore, 

 after being rendered alkaline by caustic lime and then dried, was 

 put into an iron drum and covered with cyanide solution of a 

 strength of 0'8 per cent. The solution was run off periodically, 

 and put back again into the vat. At first, as shewn by the 

 assays, the solution of the gold was rapid, it then became slower 

 and slower, and at the time when the experiment had to be 

 terminated there was still gold remaining in the ore, which was 

 slowly dissolving. The larger lumps of gold, particularly in the 

 lower part of the vat, were those which took so long to dissolve. 

 The results of the assays, on being plotted on a diagram, gave 

 a solution - curve of a very regular nature. When the cyanide 

 attained a certain gold strength it was run through the zinc box, 

 and this was repeated several times during the continuance of 

 the experiment, but it had little or no effect on the regularity of 

 the curve. 



The extraction at the end of the experiment was equal to 

 82-14 per cent of the gold contents of the ore and, had it been 

 possible to continue it, the whole of the gold might have been 

 extracted ; but the time occupied was so great that the process 

 seems to be impi'acticable. The ore contained 155 grains of 

 gold per pikul, of which 12 7;j grains were extracted. The total 

 time occupied in leaching was seventy - seven days, but it is to 

 be observed that fifty per cent of the whole gold contents of 

 the ore was dissolved in the first fourteen days of treatment. 



The hastening of the solvent action of the cyanide could be 

 effected by aeration of the cyanide solution by one of the many 

 ft)rms of agitation apparatus ; but the cost of keeping a large 

 mass of a heavy, coarse-grained substance like tin -sand in 

 motion for a period of a couple of weeks would be prohibitive. 

 The use of many chemical substances has been advocated for 

 quickening the action of the cyanide of potassium on the gold, 

 though few, if any of them, are in actual use. Amongst 

 these may be mentioned ferricyanide of potassium or other 

 ferricyanide, bromine, iodine, permanganate of potash, oxide and 

 cyanide of mercury. Whether any of these accelerators could 

 be employed with advantage in the case in point remains to be 

 proved. 



With a clean, free ore like tin - sand the process (except for 

 the slowness due to the size of flu grains of gold) worked 



