58 NITROGEN FIXATION 



more serious since from one half to two thirds of the nitrogen 

 compounds placed on the soils are lost annually in various ways, 

 especially by the leaching out of these substances by rains and 

 drainage waters, see page 44. Naturally of late years much 

 attention has been directed to devices for uniting the nitrogen of 

 the air with other elements in order to find a substitute for the 

 rapidly disappearing nitrogenous compounds. Working upon the 

 fact that nitrogen compounds are formed in the atmosphere by 

 electrical discharges, several countries are now manufacturing 

 by electrical processes large quantities of nitric acid. A much 

 more serviceable source of nitrogen compounds for fertilizing pur- 

 poses has been discovered in the production of calcium cyanamide. 



Calcium carbide (CaC 2 ), which forms acetylene gas when 

 placed in water, is produced in the manufacture of coke and when 

 heated red hot unites with nitrogen forming calcium cyanamide 

 (CaCN 2 ) and pure carbon. CaCN 2 slowly gives off ammonia 

 and consequently when mixed with the soil it becomes an ex- 

 cellent fertilizer, being quite as valuable (weight for weight of 

 the nitrogen contained) as the rapidly disappearing saltpetre. 

 Calcium cyanamide is now being extensively manufactured on the 

 Continent and it is not to be questioned that the construction of 

 nitrogen compounds will be so extended and the process so im- 

 proved as to meet the rapidly increasing demands of the culti- 

 vators of the soil. 



Much study has also been given to the nitrogen-fixing bacteria 

 as a further source of supply for nitrogen compounds. Failures 

 attended the numerous attempts to cultivate these important plants 

 with practical results until our own government through the work 

 of Moore succeeded in making cultures of the bacteria that are 

 now sold to farmers for mixing with their clover or other legu- 

 minous seeds. See Bulletin 71, 1905, U. S. Dept. of Agriculture. 

 By mixing these bacteria with leguminous seeds the farmer is 

 now able to raise a crop that contains a large amount of nitrogen 

 derived from the air and by plowing under this crop a valuable 

 nitrogenous fertilizer is added to the soil and the way is thus 

 prepared for another crop, as wheat, which is dependent for 

 nitrogen upon nitrogenous compounds. This alternation of crops 



