Catalysis or the Speeding-up of Chemical Reactions 43 



Nitrogen obtained from air is mixed with hydrogen and forced at 

 a pressure of some 200 atmospheres (3,0001b. per sq. inch) over 

 heated osmium or other catalyst. Ammonia is produced, which 

 is condensed by means of a freezing mixture, and collects in a 

 special receiver. The process is very efficient, and other cheaper 

 catalysts may be substituted instead of osmium, Avhich is very 

 expensive. Iron, it would seem, acts as a very suitable catalyst. 



A very old experiment — shown to illustrate the oxidation of 

 ammonia to nitric acid — consists in bubbling oxygen through a 

 moderately strong solution of ammonia and introducing a heated 

 spiral of platinum wire into the vapour. The platinum con- 

 tinues to glow, and white fumes of ammonium nitrate are formed, 

 due to the oxidation of some of the ammonia vapour. After 

 many years Ostwald gave a modern application to this experi- 

 ment, and built up the commercial process for preparing nitric 

 acid by the oxidation of ammonia. Platinum acts as a catalyst 

 in the process, and a mixture of air and ammonia is passed rapidly 

 over a layer of half an inch of the catalyst heated to 300°C. The 

 velocity of the mixture must be great, as otherwise the process is 

 not effective. Stoneware vessels are used in the manufacture, as 

 the hot nitric acid would attack any metal with great vigour. 



By methods such as we have outlined atmospheric nitrogen 

 is converted at a reasonable cost into ammonia and nitric acid : 

 and the Nitrogen Question is thus solved. 



Hardening of Oils. Another application of catalytic action 

 which in recent times has become important deals with the 

 hardening or hydrogenation of oils. Most vegetable oils are fluid 

 or semi-fluid under ordinary conditions. Such oils are of much 

 less value than hard fats, as they are not suitable for commercial 

 processes such as the manufacture of margarine, candles or soap. 

 On examining these vegetable oils it is found that they differ 

 from the fats in having a lower hydrogen content. They are 

 unsaturated, and are capable of taking up additional hydrogen 

 atoms. The problem of converting an oil into a more valuable 

 fat therefore centres round the most effective way of causing it 



