FREE INSTITUTE OF SCIENCE 



3 



FOOD FROM THE AIR 



phorus is most easily utilized when present as phosphate, nitrogen as am- 

 monium compounds or nitrates, potassium in one of its soluble forms. In 

 scientific agriculture large use is made of calcium phosphate, sodium nitrate 

 or ammonium sulfate, potassium chlorid or sulfate. The extent of this 

 use is shown by the immense quantities of "phosphate-rock " annually mined in 

 the United States, and the fact that in normal years about 500,000 tons of potas- 

 sium salts are imported from Germany and an equal amount of sodium nitrate 

 from Chile. The deposits of phosphate-rock in our own country are so ex- 

 tensive that no immediate fear is felt for exhaustion, but the nitrate beds of 

 Chile are thought to be comparatively near the end of their yield, and the 

 dependence upon Germany for the potassium compounds gives rise to much 

 anxiety among agriculturists in other countries. 



Governmental investigations as to methods of securing supplies of nitro- 

 gen and potassium compounds have been undertaken with much vigor, and 

 some valuable results have been obtained. So far as potassium is concerned, 

 only brief mention is in order here. The experiments of the United States 

 scientific stations have shown that several minerals that exist in the country 

 in great abundance can be utilized as sources of potassium compounds, so no 

 great anxiety need be felt on this score. 



The nitrogen problem is the serious one. A great deal of attention is 

 being given to it in civilized countries, and the war has intensified this atten- 

 tion, because the high explosives now used are mostly nitrogen compounds and 

 for their manufacture require very active forms thereof. Unlike potassium 

 and phosphorus, nitrogen does not exist in great abundance in the mineral 

 world. The sodium nitrate deposits of Chile are almost unique. A consider- 

 able formation of potassium nitrate takes place in certain tropical countries, 

 and by skilful treatment of decomposing organic matters nitrates can be 

 formed, but the process is slow and but little applicable except under stress, 

 as was the case during the French wars a century ago, when France, by reason 

 of the British blockade, was prevented from importing nitrates for the manu- 

 facture of powder. 



For a comprehension of the present phases of the food problem it is 

 necessary to understand what is called the "nitrogen cycle," that is, the suc- 

 cession of associations in which nitrogen is found in nature. Strictly speaking, 

 these associations are practically innumerable, but indication of a few distinct 

 and easily recognizable forms will suffice for the purposes of this paper. 



