METHODS OF ANALYSIS 53 



From these tests the following are deduced: 



(1). The proper strength of the solution to attain the best 

 results on the ore. 



(2). The time required for agitation, 8, 16, or more hours. 



(3). The cyanide consumption. 



These tests are quickly and cheaply made, and can be repeated 

 or modified and concordant results obtained, results which are 

 satisfactory to competent cyanide experts. 



It has been found that, for silver ores, solutions from 0.25$ 

 to 0.75$ are necessary to attack the sulphides, hence the follow- 

 ing solution strengths are recommended for silver or for gold- 

 silver ores: 0.25$, 0.30$, 0.40$, 0.50$, 0.75$. 



The lime found necessary in bottle tests to neutralize the 

 acidity is about 35$ more than is required on a full working scale. 

 Mass action in the latter case probably accounts for this. 



Should the extraction on all the series of bottles be low, put 

 on another series, using the percentage of cyanide that promised 

 the better results in the previous case, but have the ore reduced 

 to different degrees of fineness, say to pass a screen aperture of 



0.011" — About 40 apertures to the inch. 



0.0087" — About 50 apertures to the inch. 



0.0055" — About 100 apertures to the inch. 



0.0030"— About 150 apertures to the inch. 



0.0020"— About 200 apertures to the inch. 



These would show the increased extraction due to fine grind- 

 ing,* and, should the extraction remain unsatisfactory, add, after 2 

 hours' agitation, in a new series of bottles, 0.05$ to 0.10$ of the 

 weight of the ore of cyanogen-bromide. This salt will often give 

 good gold extraction on heavy sulphides or medium-grade gold 

 telluride ores, particularly when the ore is ground fine. More- 

 over, by the use of cyanogen-bromide, the cost of roasting may be 

 obviated. 



Bromo-cyanogen is a very difficult substance to obtain in the 

 West, but, in reference to its use in West Australia, Mr. Alfred 

 James states :f "It is now usually made on the spot, from im- 

 ported bromo-salts, in view of the difficulty of getting the steamship 



* The finer the ore is ground, the easier and quicker the silver sulphides are attacked by 

 weak solutions. Commercial results will thus lie between fine grinding and high 

 cyanide consumption, for, the weaker the solution the lower the cyanide consumption. 



t Engineering and Mining Journal, Jan. 7, 1904. 



