300 SMITH'S INTERMEDIATE CHEMISTRY 



is distilled for the purpose of extracting the petroleum, and much 

 ammonia, liberated at the same time, is collected. Formerly 

 it was allowed to escape, but, in the absence of a protective tariff, 

 the competition of petroleum from American and Russian wells 

 compelled economy. Now, the profit on the sale of the 

 ammonium sulphate pays the whole cost of mining and distilling 

 the shale. 



Synthetic Ammonia. The latest method of manufacturing 

 ammonia is by the direct union of hydrogen and nitrogen. 



Exactly the same difficulties are encountered in the commercial 

 operation of this reaction (Haber's process) as in the manufacture 

 of sulphur trioxide by the contact process (p. 261), but in a greatly 

 accentuated form. The union of the gases, which is exothermic, 

 is exceedingly slow in the absence of a suitable catalyst: 

 N 2 + 3H 2 - 2NH 3 + 24,000 calories. 



l n the presence of a contact agent such as a specially prepared 

 mixture of_Jron and molybdenum combination is greatly 

 hastened. Traces^ of other gases, however, such as carbon monox- 

 ide or hydrogen sulphide, must be very carefully eliminated from 

 the^e^ctin^_mixiure, since they act as poisons on the catalyst, 

 that is, they destroy or impair its activity. 



The reaction is reversible, and much more incomplete than is 

 the union of sulphur dioxide and oxygen under similar conditions. 

 Since the forward action evolves heat, the reverse action is favored 

 by raising the temperature (van't Hoff's law, p. 242), hence the 

 yield of ammonia in the equilibrium mixture becomes less and 

 less the higher the temperature employed. Thus, under one 

 atmosphere pressure, the proportions of the gases that combine 

 in a mixture of one volume nitrogen and three volumes hydrogen 

 are as follows: at 200, 15.3 per cent; at 300, 2.2 per cent; at 

 500, 0.13 per cent; at 1000, 0.004 per cent. 



The preponderance of this reverse reaction, or in other words 

 the tendency of ammonia to decompose into its constituent 





