196 Macfarlane on the Extraction of Cobalt Oxide 



1000 grains of pyrites contained 542.3 grains of sulphur, and 

 the 780 grains of the residue, only 9.98 grains Consequently 

 98.16 per cent, of the sulphur had escaped as sulphurous acid, 

 and only 1.84 per cent, had been converted into sulphuric acid 

 and combined with soda. 



That the iron oxide, as stated above, has considerable influence 

 in converting the sulphurous acid into sulphuric acid, will appear 

 from the following experiment: 59 grains of iron pyrites, 58^ 

 grains of common salt, and 234 grains peroxide of iron, (free 

 from sulphuric acid) were mixed and calcined in a mufl3e, at a 

 low red heat, until sulphurous acid and chlorine ceased to be 

 evolved. The materials weighed after calcination 336 grains, and 

 contained in 100 parts : 



Peroxide of iron 19.5 



Sulphate of soda 19.2 = 4.31 sulphur. 



Chloride of sodium. ... 1.3 by difference. 



100.0 

 The original 59 grains of iron pyrites used, contained 32, 

 and the resulting 336 grains, 14.48 grains of sulphur. Conse- 

 quently 55 per cent, of the sulphur had escaped as sulphurous acid,* 

 and 45 per cent, were converted into sulphuric acid, instead of 

 1.84 per cent, as in the experiment above described. That the 

 larger quantity of salt used did not materially contribute to this 

 result, I have proved by a series of experiments, which resulted as 

 follows : — 



1. When iron pyrites, mixed with 5 per cent, of its weight of 

 common salt, is calcined as in the last described experiment, 1.24 

 per cent, of the sulphur contained in it, is converted into sulphuric 

 acid, and combined with the soda. 



2. When 10 per cent, of salt is used, 1.84 per cent, of the sul- 

 phur is, as we have seen, converted into sulphuric acid. 



3. With 50 per cent, of salt, 2.86 per cent, of the sulphur is re- 

 tained as sulphuric acid. 



4. With 100 per cent, of salt, 7.46 of the sulphur is thus re- 

 tained. 



In this last, th<? proportion of common salt to the pyrites is 

 the same as in the experiment where peroxide of iron was used, 

 but in the latter case five times more sulphur was converted into 



• The sulphurous acid was accompanied by chlorine, in almost the 

 proportions necessary for their complete conversion of the two into sul- 

 phuric and hydrochloric acids, on being brought into contact with steam. 

 (S08+ CI + HO = SO3 + HCl). 



