Catalysis or the SjJeeding up of Chemical Reactions 41 



decline ; without her armaments her defensive and offensive 

 powers vanish ; and without sufficient foodstuffs her population 

 cannot carry on the necessarily unequal contest. In all three of 

 these we find ammonia and nitric acid, but especially the latter, 

 play an important part. Nitric acid is extensively used in 

 industries, such as the manufacture of dyestuffs and other 

 chemical products. All explosives are derived from it or its 

 salts. Food production is also intimately connected with it. In 

 this connection we must briefly examine our needs. The animal 

 body is largely composed of proteins which in the wear and 

 tear of daily life are undergoing incessant wastage and so stand 

 in need of continuous repair. The proteins are largely com- 

 posed of combined nitrogen, so animal diet must include a fair 

 amount of nitrogenous material. Animals are unable to make 

 use of free nitrogen, such as might be obtained from the air we 

 breathe ; in addition animals are unable to assimilate simple 

 compounds of nitrogen, such as nitrates or ammonium salts. The 

 nitrogen diet must be composed of organic compounds already 

 built up to the protein stage by ])lants or derived from other 

 animals. It is thus evident that animals are ultimately dependent 

 on the plant world for their supplies of nitrogen. Plants can 

 take in nitrates from the soil and convert them into vegetable 

 proteins, such as gluten of wheat. Now there are not great 

 amounts of nitrates in the soil. Some compounds containing 

 nitrogen are present in the humus of the soil ; others are carried 

 down by rains. Plants are, therefore, mainly dependent for 

 their supplies of nitrogen on the humus of the soil, which results 

 from the residues of preceding crops and the introduction of 

 animal manures. 



There is a profit and loss account on the farm, and so the 

 land gets exhausted. There is a steady drain ou the farm, the 

 crops produced being diverted to the centres of keenest demand ; 

 and so most of the foodstuffs raised, instead of being consumed on 

 the farm, are sent to the cities. Stock raised is also sold off. 

 So it is evident that there is a steady export of nitrogenous com- 



