250 FANNING AND EDDINGFIELD. 
With the nonpressure leaf filters nearly an hour is consumed in getting 
a cake upon the leaves during which time the sulphides by their high 
specific gravity, settle out of the pulp making it practically impossible 
to get a good cake. The Kelley, being a pressure filter, makes a cake 
within a few minutes and before the sulphides can settle. While there are 
other types of pressure filters, none of them seem able to give the careful 
wash necessary when working with the rich solutions associated with 
sulphides cyanidation. 
Hamilton’? advocates the use of a horizontal vacuum filter 
as follows: 
The most suitable filter would appear to be a horizontal vacuum filter, 
with sides 6 in. high, and arranged so that it might be tilted almost to 
the vertical for dumping the washed residue. A square or oblong table 
filter of this kind about 8X12 ft. would treat 500 lb. of concentrate at each 
charge, the pulp, solution, and water would be filtered to a finish in each 
case, and then the table would be tilted, the ledge on the lower side removed, 
and compressed air allowed to enter under the cake which would slide off 
towards the dump. 
At the Alaska-Treadwell mill, the concentrates, worth about 
120 pesos per ton gold value, are tube-milled and given a preli- 
minary agitation with a 2-pound lime solution. The pulp is 
then thickened by decantation and cyanided. It is then filtered 
in Kelley presses, and the solution passes to Merrill precipitation 
presses. The precipitate is treated with acid and then melted 
in an oil-burning furnace, and refined in a Faber du Faur tilt- 
ing furnace. It has been found that one 5- by 11-foot tube- 
mill can grind 88 tons of concentrates per twenty-four hours. 
The feed contains 38.5 per cent moisture and shows on 100-mesh, 
48.7 per cent; on 200-mesh, 41.5 per cent; and through 200-mesh, 
9.8 per cent. The discharge shows on 100-mesh, 10.1 per cent; 
on 200-mesh, 26.4 per cent; and through 200-mesh, 63.5 per cent. 
The tube-mills use 59-horsepower, and turn at a speed of 27 
revolutions per minute. 
As stated in the Mineral Industry: 1* 
G. E. Welcott describes the treatment of concentrates at the North Star 
and Central mills at Grass Valley, California. The concentrates are made 
on vanners and are charged into a 20X44 ft. Abbe tube-mill crushing in 
a 0.15 per cent KCN solution. The pulp from the tube-mill passes over 
amalgamation plates and then to classifiers, the spigot from which is re- 
turned to the tube-mill, while the overflow passes to tanks, where it is 
agitated mechanically. The period of agitation is six hours. During the 
treatment, the solution is twice decanted and replaced by a new solution. 
The pulp is then filtered in an Oliver filter. The concentrates treated con- 
tain from $30 to $40 per ton and an extraction of 93 per cent is made with 
a KCN consumption of 24 lbs. per ton. The approximate cost of treatment 
is $3 per ton. 
* Loc. cit., 841. “ Mineral Industry. New York (1909), 361. 
