&8 The Pliospliates of America. 



It would, of course, be folly to expect all those who are now in 

 the fertilizer trade to become owners of good pyrites mines, but 

 this fact need in nowise prevent them from erecting works near 

 such mines in order to profit by whatever advantages are to be 

 derived from using the brimstone substitutes. Let us therefore 

 examine what those advantages actually are. 



To commence with the furnace. The various forms introduced 

 during the past few years for burning pyrites in England, France 

 and Germany by Spence, Ferret-Oliver, Juhel-Maletra, Gersten- 

 hoefer and others have all been accurately described by popular 

 writers, and it will suffice for present purposes to point out that the 

 principal conditions to be realized with either lump or fines are : 



First. To generate and convey to the lead chambers a maxi- 

 mum of sulphurous acid and a minimum excess of atmospheric air. 



Second. A combustion so perfect that less than one per cent, 

 of sulphur shall remain in the cinder. 



Third. To avoid any distillation of the sulphur or the forma- 

 tion of ferrous sulphide (FeS). 



The necessary oxidation of the iron and the consequent pro- 

 portionate increase of the superfluous nitrogen carried by the air 

 in the mixture of gases, cause the volume of the latter, produced 

 by burning pyrites, to be much greater than that proceeding from 

 the combustion of pure brimstone, and it will be hence understood 

 that the proper regulation of the air-supply important under any 

 conditions is especially so when pyrites are employed. 



The gases derived from pyrites are known to move only at the 

 rate of about one foot per minute, and it therefore follows that they, 

 remain sufficiently long in the chambers to become so intimately 

 and thoroughly mixed that any attempt to give a specific direc- 

 tion, either to the manner of their entry or their exit, becomes 

 unnecessary. 



According to theory, only three molecules of oxygen need to 

 be admitted into the furnaces, two for the formation of sulphurous 

 acid and the third to transform the latter into H 2 SO 4 . For one 

 kilogramme of ordinary brimstone this would require 1500 

 grammes or 1055 litres of oxygen, or 5275 litres of atmospheric 

 air ; the amount of air necessitated by burning the same quantity 

 of sulphur in iron pyrites being, according to the same calculation, 

 6595 litres. 



In practical industry, however, Mr. Schwarzenberg has shown 

 that these figures do not suffice, and that it is necessary to intro- 



