318 SCIENCE PROGRESS. 



iooo tons, where further settling takes place, and the slimes,, 

 discharged once a week, are found to retain only about 40* 

 per cent, of moisture. The settling capacity of these vats 

 has lately been increased by the delivery of the stream of 

 pulp through a pipe of large diameter carried half-way to 

 the bottom of the vat, so that the disturbance produced by 

 additions is less marked and the settling proceeds without 

 interruption. The settled slimes are discharged from these 

 vats by a jet of water under 200 lb. pressure per square 

 inch, which rapidly disintegrates the clayey mass, so that 

 500 tons weight of slimes can be discharged in three hours 

 with little labour and at a low cost. 



In the electrolytic precipitation, it is necessary to free- 

 the liquid from all solid suspended particles to prevent the 

 electrodes from being coated with slime. This is done by 

 filtering through sand or by prolonged settlement, but the 

 clearness of the solution also depends on the solubility of the 

 anode. By keeping the current density below 0x34 amperes, 

 per square foot, however, very little corrosion of the iron 

 anodes takes place, a plate T 3 ¥ inch thick being estimated by 

 Butters to last fiveyears, while with Andreoli's peroxideof lead, 

 anode, practically no corrosion of the anode takes place at all. 



Recent details of the exact cost of treatment of slimes 

 are not available, but J. R. Williams gives it for the months 

 of April and May, 1897, at tne Crown Reef Mill as 3s. od 

 per ton including maintenance. Of this amount, cyanide 

 cost 5^d., lime 6d., and royalty for the use of electrical 

 precipitation nearly 5d. The Crown Reef Company, by 

 means of its stamp mill, cyanide plant and slimes plant is. 

 now recovering over 90 per cent, of the total gold contained 

 in the ore, at a cost of less than 6s. per ton of original ore. 



The treatment of slimes, the latest development of the- 



cyanide process, is a sign of the new order of things in the 



metallurgy of gold. Worked out with the greatest patience 



and skill by direct experiment on the substances to be 



treated, and without any thought of exclusive advantage to* 



its devisers, its main features have been at once published 



for the free use of the rest of the world, and will probably 



pass into general use with little delay. 



T. K. Rose. 



