TECHNICAL CHEMISTRY. 



gives the analyses of several samples of 

 largely in use. 



ANALYSES OF IKON PYRITES. 



313 



pyrites now 



By far the greater portion of the 850,000 tons of acid 

 made every year in Great Britain is what is termed " stone 

 acid," that is acid made from pyrites. But the employment 

 of this source of sulphur has its disadvantages. As you 

 see in the diagram, arsenic is a common ingredient of 

 pyrites, and when the pyrites is burnt the arsenic is 

 oxidized as well as the sulphur, and the trioxide of arsenic, 

 or white arsenic, as it is termed, is carried forward into the 

 chamber, and thus it comes that almost all the sulphuric 

 acid of commerce contains traces, and often far more than 

 traces, of this poisonous substance. 



Near the pyrites burners the nitre pots, or ovens, are 

 generally placed. In these a charge of 30 Ibs. of nitrate 

 of soda, or Chili saltpetre, and 22 Ibs. of sulphuric acid of 

 specific gravity 1 '75, is placed, and after the lapse of two 

 hours, when the charge is exhausted, the fused sulphate of 

 soda is run off into a pan placed outside the oven. The 

 decomposition of the nitre as shown by the equation 



2NaN0 3 + ELS0 4 - 2HN0 3 + Na 2 S0 4 

 is assisted by the heat from the pyrites burners placed 



