ASSAYING ANTIMONY ORES. 



Remaeks on the fallacy of a certain method of assaying Anti- 

 mony Ores given by some Manuals of Assaying. 



l^Sead before the Sot/al Society/ of New South Wales, 20th November, 1872, 

 by Adolph Leibius, Esq., Ph. D., Senior Assayer of the Sydney Branch 

 of the Royal Mint.~\ 



Sestcb antimony ore in the shape of sulphide of antimony 

 is frequently found in Australia, and its percentage of pure 

 antimony may become a question affecting many commercial 

 transactions, I deem it right to make a few remarks with regard 

 to a method for assaying such antimony ore. 



In Mitchell's Manual of Assaying, 3rd edition, page 432, it is 

 stated, after going into several methods of assaying different 

 antimony ores : — 



" The best method of assaying sulphide of antimony seems to 

 be one in which it is mixed with four parts of cyanide of potas- 

 sium, and heated very gently in a crucible. The heat required 

 in this case is so low, and the operation is made so quickly, that 

 none (if any) of the antimony is lost: so that this process is 

 decidedly preferable ia the way of an assay. In particular 

 cases, however, the wet method must be had recourse to." 



Now such a statement by such an authority, and from which 

 it may possibly have been copied into other treatises on assaying, 

 is very apt to mislead. 



It is not a new fact that cyanide of potassium, in decomposiag 

 sulphide of antimony, reduces a part of it to metalKc antimony, 

 but it also forms a sulpho-salt of antimony and potassium, which 

 keeps in the flux ; and therefore, the percentage of metallic 

 antimony in a sulphide of antimony ore, when obtained by direct 

 fusion with cyanide of potassium, is very considerably below 

 what it really is. 



In order to show you plainly the result of such a treatment, I 

 have here a very good antimony ore, sulphide of antimony, with 

 but little gangue ; 50 grains of it were reduced to metallic 

 antimony by an indirect process, while the other assays, each with 

 50 grains of the same sample, were made by direct fusion with 



