40 Assaying,. 
minutes and decant or pour off the clear supernatant 
liquid. Fill with water and decant in the same manner 
twice more. There remains in the flask the insoluable 
residues along with the metallic copper, etc. (3) To 
the insoluable residue (silica) and metallic copper in 
- the flask, add 5ce of nitric acid, boil for about five min- 
utes or until all red fumes have gone, let cool, then add 
10cc of ammonia, or enough to neutralize the acid. The 
solution now turns blue in proportion to the amount of 
copper present. (4) When the solution is cool add 50ce 
of water, and in case of rich ores (above five per cent. 
ore) runs into the flask from the burette enough of the 
standardized solution of cyanide of potassium to almost 
bleach the solution in the flask; having noted the 
amount of cyanide solution used, filter off the silica, 
etc., catching the light blue filtrate in a beaker. Now 
tun from the burette into this filtrate enough cyanide 
solution to bleach or discolor it. Note the total amount 
of cyanide solution used, say in this assay 20cc were re- 
quired. 
NOTE.—The Potassium Cyanide Solution is pre- 
pared as follows: Dissolve sixty grammes of the cyan- 
ide salt in one litre of water, when dissolved decant or 
ciphon the solution into a paper wrapped-bottle. The 
solution is now ready for standardizing ; this is done as 
follows: Weigh out say 250 milligrammes of pure cop- 
per and in a beaker, dissolve this in 5cc nitric acid, boil 
until red fumes have disappeared, let cool, then add 10ce 
of ammonia, let cool and add 50cc of water. Then run 
in from the burette enough of the previously prepared 
cyanide solution to bleach or discolor the copper solu- 
tion in the beaker; note the amount used, say in this 
case 15.15cc were required; then 1cc of cyanide solution 
= 250 + 15.5 = 16.13 milligrammes of copper, or since 
1000. mgrs.=1. gramme, 16.13 mgrs.=.01613 grammes. 
Therefore, 1cc of the cyanide solution will neutralize or 
