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CATALYSIS IN THE INORGANIC FIELD 



assumed for the catalytic process (the leaden-chamber process) in which the 

 nitrogen oxids act as catalyst. 



A second catalytic process for the manufacture of sulfuric acid uses 

 platinum as catalyst. Careful temperature control is one of the most impor- 

 tant factors, and the operation is conducted at about 420°. The enormous 

 heat evolution in the reaction is controlled by using it to pre-heat the mixture 

 of sulfur dioxid and air before it reaches the asbestos or other substance on 

 which the catalyst, platinum, is supported. 



Arsenic and suspended impurities soon ''poison" the catalyst. To pre- 

 pare the mixed gases, therefore, they are carefully cleaned with steam, then 

 washed, and then passed through sulfuric acid of such strength as to remove 

 all but that amount of water-vapor needed for the reaction to take place. 



Less expensive catalysts in large number have been tried, of which ferric 

 oxid as pyrites-cinders is probably the only one used commercially. Since it 

 operates best at a higher temperature and even then has a lower efficiency, it 

 may be used satisfactorily along with platinum. The hot gases are first 

 passed over the iron oxid catalyst and later over the platinum. The sulfur 

 trioxid formed is absorbed in dilute sulfuric acid. 



The third of the great industrial enterprises that rest upon catalysis is 

 the obtaining of certain nitrogen compounds by use of the nitrogen of the air. 

 Nitric acid is perhaps the most important, and its production is a national 

 necessity. It is officially estimated that the United States would need 180,000 

 tons per annum when at war with any first-class power. It is hazardous to 

 rely, in war, upon the sodium nitrate deposits of Chile, or upon the waterfalls 

 that lie upon the border of the nation with which we have more frequently 

 quarreled than with any other — the British Empire. Niagara furnishes electric 

 power at a cost sufficiently low to permit its use in manufacturing nitric acid by 

 the method of passing air through a properly constructed electric arc, but the 

 cost at its lowest is high, and only a part of the waterpower of Niagara is ours. 



By burning ammonia, nitric acid may be produced, although ordinarily 

 the change is represented by the equation : 



2NH3 + 3O -> N2 + 3H2O. 



When platinum is present, under proper conditions, the rate of another reac- 

 tion may be sufficiently changed to make it the principal reaction, namely, 



NH3 + 2O2 -^ H2O 4- HNO3. 



