280 Mr David Forbes on Chemical Examination of 



ignition, with nitric acid, and again to apply heat, so as to 

 ensure that no de-oxidation could take place. 



The solution from which the iron had been separated was 

 now precipitated by carbonate of potash, but the resulting 

 oxide of manganese precipitated was so small as hardly 

 possible to determine it with exactness, and was therefore 

 not collected. It was, however, sufficient to prove the 

 existence of a trace of manganese in the ore, which possibly 

 would amount to about -1 per cent. 



The quantities found were as follows : — 



Mineral employed, . 20*58 grains. 



Obtained Sulphate of barjtes, . 26*77 „ 



„ Free sulphur, . 1*36 „ 



„ Sesquioxide of iron, ' . 3*28 „ 



„ Silicious residue, . '79 „ 



„ Oxide of copper, . 15*39 „ 



And the per-centage composition calculated from these results 

 is as follows : — 



100*00 100*00 



If we now deduct the silicious matter and loss in analysis 

 from the amount employed, and allow the deficiency to be 

 equally distributed over the other constituents, we have as the 

 composition of the pure sulphuret— 



Sulphur, . 25-69 

 Copper, . 62-64 

 Iron, . 11-67 



100-00 



For the sake of comparison I subjoin the following analyses, 

 which give almost the same results : — 



