jQ TRANSACTIONS OF WAGNER 



FOOD FROM THE AIR 



with production of heat, hence the temperature increases. Care must be taken 

 that this increase does not go beyond 1400°, as the reaction, Hke that of the 

 oxidation of nitrogen, is reversible, and the cyanamid will be decomposed. 



The electric method has some advantages over that by heating in re- 

 torts. The combination once begun is carried on by the heat produced in the 

 reaction, hence the current may be cut off. Superheating is not likely to occur 

 and the action proceeds from without inward, which causes the product to 

 shrink from the walls of the containers. 



On the large scale, as at Odda, Norway, the process requires about thirty 

 hours. 



At several plants on the continent of Europe the direct heating process is 

 used, but some practical difficulties have developed. The most serious is that 

 the heating cannot be so easily controlled and hence loss of cyanamid may 

 occur, also the mass adheres to the walls of the retorts and has to be hacked 

 out. It has been found that the addition of moderate amounts of calcium 

 chlorid or calcium fluorid will diminish these conditions. These substances 

 appear to act especially by reducing the temperature necessary for the action, 

 probably by rendering the carbid fusible at a lower temperature. The product 

 of this modified method contains some calcium chlorid, which makes it liable 

 to absorb moisture — a notable disadvantage. 



Calcium cyanamid is marketed in a finely powdered form, often under the 

 term "nitrolim." 



It will be seen that the cyanamid processes differ from the nitrogen- 

 oxidation processes by the fact that the former require practically pure nitro- 

 gen, at least, nitrogen with no appreciable amount of oxidizing substances or 

 moisture. In the oxidation processes the raw material is air, which is obtain- 

 able in unlimited amount. The production of the pure nitrogen necessary for 

 the cyanamid method is largely by the liquefaction of air and separation of the 

 nitrogen and oxygen by fractional evaporation. In some works the nitrogen 

 is obtained by passing air over hot copper, by which the oxygen is removed. 

 The copper is then recovered by heating the oxid in a current of water-gas. 



Improved air-liquefaction methods yield nitrogen containing not over o.i 

 per cent, of oxygen. 



The fertilizing action of calcium cyanamid is dependent essentially upon 

 its power of yielding ammonium compounds under the influence of moisture, 

 with probably the coincident action of soil bacteria. Several stages of the 



