FREE INSTITUTE OF SCIENCE 



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FOOD FROM THE AIR 



reaction may occur, but the final result is expressed by the equation CaN2C+ 

 3H20->2NH3+ CaCOa. 



From this reaction it is obvious that the material may be used as a source 

 of ammonium compounds. For this purpose it is acted upon by superheated 

 steam. Other derivatives of calcium cyanamid find application in color and 

 explosives industries that do not need consideration here. 



FIXATION OF NITROGEN AS AMMONIA 



Many sources of ammonium compounds are available. They are found 

 in notable amount in the products of the putrefaction and destructive dis- 

 tillation of many animal and vegetable materials. In these cases they are the 

 result of decomposition of nitrogenous substances by complex reactions almost 

 wholly unknown, and as they do not involve the fixation of atmospheric nitro- 

 gen, do not come within the scope of this essay. 



As ammonium compounds can be transformed into many other forms with 

 comparative ease, their abundant supply is desirable, hence much attention 

 has been given to utilization, for their production, of the immense stores of 

 nitrogen in the atmosphere. 



For their production by the direct action of nitrogen and hydrogen (syn- 

 thetic ammonia) the two gases in a high state of purity are obtained by well- 

 known industrial methods. Their union is accomplished by the joint action of 

 heat, pressure, and a catalyst. The last mentioned is a substance that promotes 

 combination without permanently entering into the compound formed, hence 

 a small amount of it will suffice to bring about combination of large amounts of 

 the other substances. 



The combination of nitrogen and hydrogen in pure dry condition gives 

 ammonia, NH3, which is readily absorbed by water and acids. The volume of 

 ammonia is less than that of the free gases (a mixture of one volume of nitrogen 

 and three volumes of hydrogen produces two volumes of ammonia). The 

 reduction of volume causes the reaction to be favored by pressure. 



The scientific and practical investigation of the production of synthetic 

 ammonia is due to Haber and Le Rossignol, who in 1913 published a paper in 

 Zeit. f. Elektrochemie. They found that by employing a pressure of about 200 

 atmospheres (3000 pounds to the square inch), a temperature of between 500° 

 and 700° and passing the gases over a catalyst, from three to twelve per cent, 

 of ammonia could be obtained. 



