900 



SCIENCE 



[N. S. Vol. XL. No. 1042 



concerning the possibility of a future famine 

 in the world's supply of nitrates and other 

 nitrogen compounds. At that time the supply 

 of these salts was largely confined to certain 

 beds of guano and Chile saltpeter. During 

 the past few years most important advances 

 have been made in our knowledge of the fixa- 

 tion of atmospheric nitrogen, and some of the 

 processes have been placed upon a purely com- 

 mercial basis. 



In addition to drawing on the air directly 

 for nitrogen it has been found that large 

 amounts of ammonia and other nitrogen com- 

 pounds may be obtained as by-products from 

 coal and peat in connection with the manu- 

 facture of coke, illuminating gas and the 

 metallurgy of iron. The treatment of various 

 shales, peats, silts and organic refuse often 

 yields nitrogen compounds. The nitrogen in 

 these substances has probably been derived 

 from the atmosphere by one or more of the 

 processes which will now be described. 



The amount of nitrogen that enters into 

 the plant and animal growth (" nomadic " 

 nitrogen) has been estimated to be about 20 

 gm. per square yard of land. Part of this is 

 being constantly changed into nitrogen gas by 

 the action of nitrifying and dentrifying bac- 

 teria. In nature an equilibrium is maintained 

 between the action of these bacteria and the 

 oxidization of nitrogen in the air by means of 

 electrical discharges and the action of plants, 

 such as clover. The natural processes of fix- 

 ing nitrogen are therefore electrical and by 

 the action of bacteria in the legume crops of 

 clover and similar plants. In former geolog- 

 ical times certain nitride and other chemical 

 compounds may have been formed directly 

 with the air nitrogen, but it is doubtful if any 

 such direct chemical reactions take place at 

 present. 



The natural oxidation of nitrogen by elec- 

 trical discharges takes place during electrical 

 storms, the aurora discharges at high levels 

 and possibly in a slight degree in the bom- 

 bardment of the higher strata of air by cathode 

 and similar rays, ultraviolet light, and pos- 

 sibly by other radiations. The disintegration 

 of radium and thorium products yields a 



small amount of oxides of nitrogen. It has 

 been estimated that in this way about 100,- 

 000,000 tons of fixed nitrogen is carried to the 

 earth every year by rain water. 



The other natural method of fixing atmos- 

 pheric nitrogen is that of the action of bac- 

 teria in the root nodules of the clovers, peas, 

 vetches and other legumes. The chemical 

 processes are very complicated and are at pres- 

 ent unknown. This process is, however, of tre- 

 mendous importance to the farmer and is 

 probably the cheapest method now known of 

 obtaining nitrogen as a fertilizer. This 

 method is, however, quite expensive in that 

 clover seed is expensive and the raising of a 

 crop of clover requires attention, time and 

 the exclusion of other crops. On the poor soils 

 where humus is the most needed it is found 

 very difficult to get clover to grow. Eestora- 

 tion of fertility to run down soils by this 

 method is therefore slow and expensive. 



The commercial methods of manufactur- 

 ing nitrogen salts includes the cyanamide 

 process, the direct synthesis of ammonia, the 

 various nitride processes of making ammonia 

 and the electrical methods of oxidizing ni- 

 trogen. 



A process that is being used commercially 

 is that of treating calcium carbide with ni- 

 trogen gas, thus yielding cyanamide which 

 itself makes a good fertilizer. Although the 

 reactions are known to be complex, they may 

 be represented as regards the end products as 

 follows : 



CaO + 30^ CaC^ -|- CO, 

 CaC^ -I- Ni -^ CaON, -f- C. 



The latter reaction begins at 1000° 0. or at 

 even lower temperatures. The IsT, may be pre- 

 pared by the Linde process or by passing air 

 over hot copper. According to Caro the energy 

 consumption for fixing one ton of nitrogen 

 (including making the CaO,, azotising, ma- 

 chine driving, grinding, charging, air lique- 

 faction) is less than 3 H.P. years. 



The direct combination of nitrogen and 

 hydrogen into ammonia is very successful 

 when done on a small scale with pure gases 

 but, so far as is generally known, this process 

 is not being worked on a large scale. A Ger- 



