36o JOSEPH STRUTHERS 



following proportions: For the treatment of phosphate rock, 

 50 per cent; for refining crude petroleum, 38 per cent; and for 

 use in the chemical trade, 12 per cent. 



In making sulphuric acid from pyrite, pieces of the mineral 

 ranging in size from several inches in circumference to extreme 

 fineness are burned with access of air in a furnace, of which 

 there are many forms, each suited for some special physical 

 or chemical characteristic of the ore. As a result of the burn- 

 ing, or oxidation, the sulphur content of the pyrite or pyritifer- 

 ous ore is converted into sulphur dioxide gas. When the ore 

 contains over 30 per cent of sulphur, the heat generated by the 

 oxidation of the sulphur is sufficient to maintain conibustion 

 without fuel. The sulphur dioxide gas produced in this man- 

 ner is purified, and subsequently converted into sulphuric acid, 

 either by the chamber process, in which the oxidation is ac- 

 complished by nitric oxide gases and steam, or by the contact 

 process, previously described. 



