TJie Phosphates of America. 85 



of the latter, and sulphur dioxide is formed (SO 2 ). If this gas be 

 brought into contact with nitric-acid vapor (HNO 3 ) and steam 

 (H 2 O), a combination takes place resulting in the formation of sul- 

 phuric acid and nitric oxide, thus : 



3 SO 3 + 2 HNO 3 + 2 H 2 O = 3 H 2 SO 4 + 2 NO. 



The nitric-acid vapor is produced by heating a mixture of nitrate 

 of soda and oil of vitriol in an iron pan contained within the brim- 

 stone or pyrites burners, and it is carried into the lead chambers 

 simultaneously with the sulphur dioxide by means of a well-regu- 

 lated air current. Reduced, as we have seen, to nitric oxide, it 

 does not remain in this form, but immediately combines with the 

 free oxygen introduced by the air-current and becomes nitric per- 

 oxide (NO 2 ). Assisted by the presence of steam, it thus constantly 

 enacts the part of an oxygen-carrier to the sulphur dioxide, as 

 may be gathered from the following figures: 



NO + O = N0 2 



Nitric oxide -j~ Oxygen = Nitric peroxide 

 and 



NO 2 + SO 3 + H 2 O = H 2 SO 4 + NO. 



Nitric peroxide -f- Sulphur dioxide -|- Steam. 



And so oxidation and reduction go on, and the circle of opera- 

 tions is complete and continuous. 



The air of the atmosphere contains about seventy-nine per cent, 

 of nitrogen and about 20.90 per cent, of oxygen in every 100 vol- 

 umes. This nitrogen plays no part at all in the changes we have de- 

 scribed, and it hence follows that the required oxygen is accompa- 

 nied by four times its volume of an inert gas which merely serves to 

 fill up the chamber space and which calls for immediate and steady 

 removal in order that the working elements may have fair play. At 

 one time a simple chimney arranged at the end of the works, oppo- 

 site to that at which the gases enter the chambers, was deemed 

 sufficient, but it was soon discovered to the cost of the manufact- 

 urer that the nitrogen, in itself escaping, carried off with it a 

 large share of the nitric oxide. As the preservation of this latter 

 gas is so important a factor in the economy of the industry, means 

 had to be devised whereby it could be saved without inconvenience, 

 and these means were duly provided and are now universally em- 

 ployed, as we shall presently see. 



From the commercial standpoint of economical production, the 

 chief questions that have to be seriously considered by fertilizer 



