

ARTIFICIAL FERTILIZERS 189 



problem of securing the necessary substances in quantities 

 sufficient to satisfy the demand bids fair to be serious. But 

 modern chemistry is at work on the problem, and already it is 

 possible to make commercially some nitrogen compounds suit- 

 able for absorption by plant roots. 



Phosphorus is obtained from bone ash and from phosphate 

 rock which is widely distributed over the surface of the earth. 

 Bone ash and thousands of tons of phosphate rock are treated 

 with sulphuric acid to form a phosphorus compound which is 

 soluble in soil water and usable by plants. 



The other important ingredient of most fertilizers is potash. 

 Wood ashes are rich in potash and are a valuable addition to 

 the soil. But the amount of potash thus obtained is far too 

 limited to supply the needs of agriculture ; and for many years 

 the main sources of potash have been the vast deposits of 

 potassium salts found in Prussia. 



Although Germany up to 1915 furnished the American 

 farmer with the bulk of his potash, it will probably not do so 

 in the future. In 1911 an indirect potash tax was levied by 

 Germany on her best customer, the United States, to whom 

 15 million dollars' worth of potash had been sold the preceding 

 year. This led Americans to inquire whether potash could not 

 be obtained at home. When the German supply was cut off 

 by the Great War, the search for other supplies was redoubled. 



Geologists say that long ages ago an ocean covered Germany, 

 that the waters of the ocean slowly evaporated, and that the 

 various substances in the sea water were deposited on the ocean 

 bed in thick layers. The deposits thus left by the evaporation 

 of the sea water gradually became hidden by sediment and soil,* 

 and lost to sight. From such deposits, potash is obtained, 

 Geologists tell us that some of our own land in the West was 

 once covered by an ocean, and that most of the waters evapo- 

 rated and disappeared from it very much as they did from 



