280 DISCOVERY OH. 



worse and worse. We raised what we could on a small patch 

 of sandy land, and kept trying to find out what we could grow 

 on this black bogus land. Sometimes I helped the neighbours 

 and got a little money, but my wife and I and my older children 

 have wasted twenty years on this land. Poverty, poverty, 

 always ! How was I to know that this single substance which 

 you call potassium was all we needed to make this land pro- 

 ductive and valuable ? " 



Without the artificial supply of nitrogen to the soil, it 

 would be practically impossible to grow sufficient wheat 

 to supply the needs of the present inhabitants of the 

 earth who use it for food. The nitrogen is obtained 

 chiefly from nitrate of soda mined in Chile, but these 

 deposits are by no means inexhaustible. Fortunately, 

 science has come to the rescue ; and nitrogenous ferti- 

 lisers are now produced on a large scale from the nitrogen 

 of the atmosphere. The chief source of potash, which 

 greatly increases the fertility of certain soils, is immense 

 saline deposits in the Stassfurt district of Germany. 

 The deposits were discovered about the middle of the 

 nineteenth century, and were at first regarded as useless, 

 but now nearly all the potash required in the arts as 

 well as in agriculture is obtained from them. 



In addition to nitrogen and potash, most plants require 

 phosphorous compounds or phosphates to stimulate 

 their development and quicken their ripening. It was 

 an English country gentleman, Sir John Bennet Lawes, 

 who, in 1 834, guided by the researches of De Saussure 

 on vegetation, showed by experiments the value of this 

 constituent when added to the soil, and discovered a 

 means of producing any quantity of it. Mineral phos- 

 phates, such as apatite, are usually too insoluble to have 

 any practical value in agriculture, but Lawes found that 

 if they were previously treated with sulphuric acid (oil 

 of vitriol), a " superphosphate " was produced in which 



