THK XITEOGEX PROBLEM. 10-'^ 



the last being- helium, which was liquefied in 1908 by 

 Professor Kamerliugh Dimes at the University of Ley den. 

 Linde and Claude worked out tlie problem of their large scale 

 manufacture, and so provided a most convenient and suitable 

 method for procuring- the necessary nitrog-en from the 

 atmosphere. What this means will be realised from the fact 

 that at Niagara 2,000,000 cubic feet of nitrogen are required 

 and obtained per day. Lime is prepared by the usual method 

 of burning limestone in kilns, mechanical arrangements of the 

 most modern type being* installed for charging', discharging- 

 and grinding to ensure economical working. 



Coke is manufactured from coal, the gaseous distillate 

 being also utilised in the lime kilns, or, if the old copper 

 method of obtaining nitrogen from the air be in use, in the 

 reduction of the oxide formed. The lime and coke are then 

 burnt in large electric furnaces of 10 to 20 tons capacity, 

 working with a low voltage and high amperage to form a higii- 

 grade calcium carbide, which is tapped from the furnaces at 

 regular intervals into trays and allowed to cool in a current 

 of air. The material, containing- about 80 per cent, pure 

 carbide, is then ground to a fine powder in a gas-tight 

 apparatus filled with nitrogen, an operation otherwise not 

 unattended with danger owing to the explosive power of 

 carbide dust, and is then placed in the cyanamide ovens of one 

 to two tons capacity, heated electrically, and nitrogen passed 

 in. Great care has to be exercised in this operation, since the 

 reaction is reversible and strongly exothermic, which necessi- 

 tates but little electric energy to keep t]ie temperature up to 

 800° C. to 1,000° C. required^ After 80 to 40 hours the hard 

 cake of cyanamide is removed, cooled, and then ground to a 

 fine powder in an atmosphere of nitrogen in rock-breaking 

 machines. 



To prepare it as a fertiliser, it is partly slaked to ensure 

 decomposition of any carbide which has been left undecom- 

 posed, then stored in silos until ready for packing and trans- 

 portation. In addition to its use as a direct plant food, 

 cyanamide is also used for case hardening- iron goods, as a 

 source of ammonia, and, when heated with a flux such as soda 

 or common salt, for the preparation of crude cyanide. In the 

 production of ammonia the reaction is carried out in steel 

 autoclaves of 1,000 cubic feet capacity almost filled with water 

 or alkali solution, the cyanamide being run in as a fine powder 

 with vigorous stirring, after which superheated steam is 

 admitted up to four atmospheres pressure. Since the reaction 

 itself is exothermic, the evolution of ammonia soon commences, 

 and the steam ammonia mixture given off is rectified, yielding 

 an aqueous solution of ammonia of great purity. 



Although the reaction between calcium carbide and 

 nitrogen appears simple when written down as an ordinary 

 chemical equation, CaCo + Nj ^N.Ca.ClST. + C, several investi- 

 gators, including Professor Haber, have attempted to 

 determine the conditions of equilibrium at varying- tempera- 

 tures and pressures without success. Pure carbide does not 

 react, according to Moissan, with nitrogen, whereas the 



