42 A. Killen Macbeth on 



pounds which necessarily exhausts the soil. To carry the story 

 on, it need but be stated that the nitrogenous compounds sent 

 into the city for consumption ultimately find their way in 

 sewage to the sea, and so are lost. 



The researches of Lawes and Gilbert and other agricultural 

 chemists showed that the application of nitrate of soda or sul- 

 phate of ammonia greatly increased the yields of crops. The 

 practice so introduced was greatly extended, and an enormous 

 demand grew up for these artificial fertilisers. The chief source 

 of sulphate of ammonia is the bye-product produced in the gas 

 works throughout the country, and this is very limited. The 

 chief source of nitrates was the nitre beds in Chili where sodium 

 nitrate deposits were found. The amount of sulphate of 

 ammonia is small, and it was found that the demand on the 

 Chili beds was so great that calculations predicted that they 

 would be exhausted in the year 1923. Considerations of this 

 nature gave rise to what was known as the nitrogen question ; 

 and Sir William Crooks, speaking at the British Association 

 at Bristol in 1898, for reasons such as we have hinted at 

 above, said : " England and all civilised nations stand in deadly 

 peril of not having enough to eat. As mouths multiply food 

 resources dwindle." And further he added : " I hope to point a 

 way out of this colossal dilemma. It is the chemist who must 

 come to the rescue of the threatened communities. It is through 

 the laboratory that starvation may ultimately be turned into 

 plenty." 



Efforts then were made to prepare nitrates and other com- 

 pounds of nitrogen on a commercial scale. In the atmosphere 

 there are practically unlimited amounts of nitrogen ; but nitrogen 

 is a very sluggish element, combining but slowly with most other 

 elements. It can be made to unite with oxygen under the in- 

 fluence of electrical discharge, but this is not a catalytic process, 

 and so does not concern us here. It can, moreover, be made to 

 combine with hydrogen by the influence of certain metals, and 

 this forms the basis of the Haber process for producing ammonia. 



