236 CHARLES E. MUNROE 



tified with the development of the cyanide process from its 

 introduction into this country in practical form, and has had 

 extensive professional experience in South Africa, says that 

 in our more modern plants the electrolytic and zinc proc- 

 esses are now used in combination for the recovery of the 

 metal from cyanide solutions. The solution is first cleaned 

 by the electrolytic process. It extracts from 90 to 94 per cent 

 of all the products, including practically all of the copper. 

 About 8 to 9 per cent of the electric box capacity is then 

 filled with zinc, which, aided by the electric current, removes 

 the small quantities of gold and silver remaining. By this 

 combination the zinc is constantly at its best, as everything 

 that would injure the surface of the zinc as a precipitating 

 surface has been eliminated by the previous electrolytic 

 treatment. At Butters' mines, in Salvador, an extraction 

 of about 99 per cent of the values in solution is made on regular 

 monthly runs. This process is used also at Virginia City, Nov., 

 and at Minas Prietas, Mexico. 



The methods used in the Witwatersrand have been de- 

 scribed recently by John Hays Hammond, as follows: 



''The following description applies to the treatment of 

 ores in the pyritic zones. Ores from the upper (oxidized) 

 horizons of the reefs, which constitute but a small percentage 

 of the ores treated, require a slight modification of the process. 



"The ground near the mines is level, and does not permit 

 transportation by gravity; consequently the ore must be 

 first elevated into the ore bins at the mill, and the tailings 

 leaving the mill must be elevated for treatment by the cyanide 

 process. This is done either by tailing pumps or, preferably, 

 by tailing wheels. These are from 40 to 50 feet in diameter, 

 and discharge the tailings into a launder, which, with a grade 

 of about 3.5 per cent, carries them to the cyanide works. The 

 auriferous pyrites are, to a large extent, taken out as concen- 

 trates by means of Spitzlutten (hydraulic classifier). About 

 10 per cent of the mill pulp recovered in this way consists 

 of pyrites with coarse sand, a concentration of 10 to 1 being 

 obtained. These concentrates are taken to tanks for separate 

 treatment. From two to three weeks of treatment is re- 

 quired in order to obtain from this material a recovery of 



