72 ASSAYING ANTIMONY OEES. 



cyanide of potassium. You see at a glance the difference in tlie 

 size of tlie antimony buttons : — 



No. 1, done by indirect fusion, weighs S2-4>2 grains = 61"84i per 

 cent, of pure antimony. 



No. 2, done by direct fusion, weighs 17'24 grains z= 34*48 per 

 cent, of pure antimony. 



No. 3, done by direct fusion, 17'16 grains z= 34"32 per cent, of 

 pure antimony. 



It is not an uncommon thing to accept two identical results of 

 one sample as a proof of the correctness of an analysis ; but 

 you see here, that such is only true when the method employed 

 is free from error. It is singular that tliis sulpho-salt should 

 form in such regular proportions, since in several experiments 

 with different quantities of sulphide of antimony, I always 

 obtained 34 per cent, of antimony from an ore containing in 

 reality 65 per cent. Pure sulphide of antimony contains 72*77 

 per cent, of antimony. It is not my object to do more than point 

 out this fallacy of the direct fusion with cyanide of potassium. 

 I may observe, however, that in cases where a sulphide of 

 antimony ore is free from lead or other metals, the objection 

 of direct fusion may be overcome by evaporating 30 or 50 grains 

 in a small porcelain crucible with strong nitric acid, and heating 

 very carefully until the sulphate of antimony is completely 

 converted into oxide of antimony, sulphuric acid being driven 

 off; this oxide can then readily be fused with cyanide of potas- 

 sium. Of course other antimony ores, containing lead, copper, 

 &c., or antimony alloys, require different ways of analysis, the 

 choice of which must be decided in each case, according to the 

 substance from which the antimony requires to be separated. 

 But the object of the foregoing remarks being merely to 

 point out a possible source of error, I need not here enter into 

 a description of the best methods for assaying other antimony 

 ores. 



