Assaying. 41 
indicates the presence of .01613 grammes of pure copper. 
Now, since in the assay of the ore, 20cc of the cyan- 
ide solution were used, it is evident that there is present 
.01613 X20=.32260, or 32.26 per cent. of pure copper in 
the ore. 
Note.—This .01613 is called the standard factor 
and it should be labled on the cyanide solution bottle for 
future reference. 
If two litres of water, instead of one, or 30 grammes 
of the cyanide salt, instead of 60 grammes, had been 
used in making up the solution the standard factor 
would have been .01613 + 2 = .00806. A solution of the 
latter strength is preferable, since the error in reading 
the burette is only one-half of that in the former case. 
In practice, where a great number of assays are to be 
made at one time the most convenient solution is one of 
which 1ec=.01 grammes, or 10 milligrammes of copper, 
or which is the same thing, lec of cyanide solution 
equals 1 per cent. copper. Such a solution may be made 
by diluting the above solution to 1.613 litres of water. 
Note.—The strength of the solution will depend 
upon the purity of the cyanide salt used. 
SECOND METHOD. 
If there is no zinc, nickel or cobalt present 
in the ore, the following rapid method is 
preferable and in general gives more satisfactory re- 
sults: ‘Take ore, 1 gramme, and boil in flask as before 
with Yee nitric acid, 5ce sulphuric acid and about 1. 
gramme potassium-chlorate added a little at a time (if 
the ore is a heavy sulphide), boil until the red fumes 
have cleared away (or until all the copper is in solu- 
tion), then let cool and add 15cc of ammonia (or enough 
to neutralize the acid) and 50cc water, let cool and run 
in enough cyanide solution to almost bleach the solution 
