44 Laboratory Tests. 
the work, wash and dry samples and assay leached pulp. 
The difference between the assay of the leached pulp 
and the assay of the ore before treatment should equal 
the amount of gold recovered, or in solution. An ap- 
proximate determination of the amount of cyanide con- 
sumed per ton of ore may be made as follows: Dissolve 
in*two litres of water fourteen grammes potassium-iod- 
ide and seven grammes metallic iodide. Dissolve one 
gramme of cyanide in one litres (1,000 gms.) of water; 
this corresponds to two pounds of cyanide to the ton of 
water. Measure out 30cc of this cyanide solution, add a 
few drops of starch solution (starch rubbed and dis- 
solved in water) and titrate with the iodide solution 
until a bluish yellow color is seen. Now divide the two 
pounds (cyanidé im one ton of water) by the number of © 
(cc) iodide solution required or used, the quotient indi- 
cates the number of pounds of cuanide per ton of water 
that each (cc) of the iodide solution is equal to. This 
quotient is called the standard factor and it should be 
labeled on the iodide solution bottle for future refer- 
ence. After agitating the assays in the bottles with zine 
shavings for a few minutes, filter and measure out 30ce 
of the solution, titrate as above and multiply the num- 
ber of (cc’s) of the iodide solution used by the standard 
factor, the product is equal to the number of pounds of 
cyanide in a ton of the solution tested.. Knowing the 
strength of the cyanide solution before and after using, 
the difference, therefore, equals the loss in treatment, or 
the amount consumed. In cyanide mill practice it is 
customary to leach the ore first with the strongest solu- 
tion for the proper time, then with a weaker solution. 
After this it is washed with water, running all solutions 
after being filtered through boxes filled with zinc shay- 
ings. In these boxes the gold and silver is precipitated, 
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