in] , FOOD SUPPLY 33 



manufacturers' waste products, etc. or by growing 

 leguminous crops. Since the loss of nitrogen is con- 

 siderable recourse must often be had to one of 

 these methods, and grave doubts have at times been 

 expressed as to how long the world's supply of 

 nitrogen compounds would last. Of late years, how- 

 ever, it has been found practicable to make nitrogen 

 compounds from the inexhaustible stock of nitrogen 

 in the air; the world's supply of nitrogen manures 

 can therefore be increased whenever necessary, and 

 the dreaded nitrogen famine has been relegated to 

 the time when the energy supply shall give out. 



Phosphates are supplied in the form of bones, 

 guanos, basic slag and rock phosphate. Most soils 

 contain insufficient to satisfy the large crops pro- 

 duced by the modern farmer; frequent additions 

 are therefore necessary, especially under conditions 

 of high farming. The losses are not as serious as 

 those of nitrogen. There is practically no washing 

 out; the agricultural chemist can still detect the 

 phosphates added to the lands round the cities of 

 ancient Egypt. Nevertheless there is a steady and 

 continuous loss in the crops which has to be made 

 good. There is no way of adding a single ounce to 

 the world's stock of phosphorus compounds, and this 

 is being drawn upon even now to the extent of some 

 millions of tons each year, while the demand increases 

 steadily as time goes on. If some day the supply 

 R. 3 



