238 CHARLES E. MUNROE 



weak solution 0.10 per cent of KCy. In the Siemens-Halske 

 process the solutions are weaker, namely, the strong solution, 

 0.10; medium, 0.02; and weak, 0.01 per cent of KCy. 



"The treatment requires from four to seven days. From 

 130 to 150 tons of solution are usually employed for 100 tons 

 of sand. After being allowed to drain, the sands are dis- 

 charged through bottom discharge doors into trucks, in which 

 they are removed to residues or taihngs heaps. Here, again, 

 elevation is necessary, on account of the flatness of the country, 

 and is usually effected by the endless rope system. These 

 taihngs heaps are conspicuous throughout the mining dis- 

 trict. By reason of the heavy winds prevaihng at certain 

 seasons of the year, they are becoming a great nuisance, 

 and the question of their future disposition is one of the prob- 

 lems for the mining engineer. 



''The cyanide solution, after being drawn off from the 

 leaching tanks, is taken to the precipitation boxes. The 

 gold from the strong solution is precipitated in one set and 

 that from the weak solution in another set of boxes. Pre- 

 cipitation is effected by either the MacArthur-Forrest or the 

 Siemens-Halske process. 



'Tn the MacArthur-Forrest process the gold is pre- 

 cipitated by zinc, the solution passing upward through a 

 succession of compartments, in which are placed zinc shav- 

 ings or filings, resting on a movable tray of coarse screening. 

 About twenty precipitation boxes, 20 feet by 3 feet by 3 feet 

 9 inches in size, are used. The gold bearing solution is 

 brought into close contact with the zinc, causing the deposition 

 of the gold, partly as a metalhc coating on the zinc and partly 

 as gold slimes, which sink to the bottom of the box. As 

 the zinc is gradually dissolved by cyanide more is added. 



"Once or twice a month the boxes are emptied, and the 

 gold slimes are treated with dilute sulphuric acid, then dried 

 and melted in crucibles. The dried slimes contain about 

 15 to 20 per cent of gold, and after fluxing with borax and 

 soda an ingot of 0.750 to 0.800 fineness in gold and 0.100 

 in silver is obtained. The slag, carrying from 5 to 50 ounces 

 of gold per ton, is usually sold to smelters. 



"This precipitation process yields satisfactory results 



