METALS AND CYANIDE PROCESSES 237 



from 90 to 95 per cent of the gold it contains. A solution 

 of about 0.25 to 0.3 per cent of cyanide of potassium is used. 

 After passing over the Spitzlutten the tailings are run to 

 Spitzkasten (pointed boxes), where the heavier sands are 

 allowed to settle, while the lighter material (slimes) over- 

 flows, and is carried to the slime works for special treatment. 

 The sands which settle in the Spitzkasten, representing about 

 70 per cent of the battery pulp, are continuously discharged 

 by pipes leading from the bottom of the box, and are delivered 

 by a hose or by an automatic revolving distributor to settling 

 tanks, into which they are so fed as to be as thoroughly mixed 

 as possible. This separation of the sands from the slimes has 

 to be carefully made, so as to remove all clayey substances, 

 the presence of which would otherwise prevent rapid perco- 

 lation of the solution and the free access of atmospheric oxy- 

 gen, which is essential to the solution of gold by cyanide. 



'^^Most of the modern plants have a system of double 

 treatment, the tailings being settled in the settling tanks, when 

 they are treated, after being allowed to drain, with a weak 

 solution of cyanide of potassium. This addition of the cyanide 

 of potassium is made rather for the purpose of saturating 

 the sands with the solution than for thorough leaching, which 

 would be difficult on account of the packing of the sand as 

 they are settled, rendering percolation difficult. After the 

 solution has been drained off, the sands from the settling 

 tanks are discharged into the leaching tanks, placed immedi- 

 ately below the settling tanks, from which they are filled 

 from discharge doors on the bottom of the latter. For a 

 200-stamp plant 16 steel settling and 16 steel leaching tanks 

 are usualty employed. From 3 to 4 settling and leaching 

 tanks are used for the treatment of the Spitzlutten concen- 

 trates above described. The settling tanks are usually 40 

 feet in diameter and 9 feet high. The leaching tanks have the 

 same diameter, but usually a foot less height. The capacity 

 of these tanks is about 400 tons of pulp each. 



''In the leaching tanks the pulp is subjected to three 

 treatments with cyanide of potassium. Where the Mac- 

 Arthur-Forrest process is used, the strong solution contains 

 0.25 per cent, the medium solution 0.2 per cent, and the 



