42 FERTILISERS CONTAINING NITROGEN [chap. 



heating a mixture of calcium carbide and chloride in a 

 stream of pure nitrogen at about 750° C. The product, 

 known as stickstoff-kalk, is a black powder containing 

 over 20 per cent, of nitrogen and about 10 per cent, of 

 calcium chloride, together with a considerable amount 

 of free lime. As a manure stickstoff-kalk behaves in all 

 essential respects like the kalk-stickstoff oi v^YiXoh a more 

 detailed description has been given. 



The other method of bringing nitrogen into com- 

 bination — that of effecting its union with oxygen at 

 the temperature of the electric arc — has received con- 

 siderable attention, and forms the base of at least two 

 working processes. It will be remembered that when 

 Sir William Crookes in 1898, in his British Association 

 address, warned the world of the rapidly progressive 

 exhaustion of its supplies of combined nitrogen, it was 

 to the union of nitrogen with oxygen that he looked 

 for the future supply of combined nitrogen for the 

 wheat crop, and he showed experimentally how the 

 two gases would burn together at a very high tempera- 

 ture. Not enough heat, however, is given out by the 

 flame to bring more gas up to the ignition point, hence 

 the flame is only continuous as long as external energy 

 is poured in. 



Calculating from the best results Lord Rayleigh 

 had obtained in bringing nitrogen and oxygen into 

 combination by the electric spark, Crookes decided that 

 if electricity could be generated at one-seventeenth of 

 a penny per Board of Trade unit, as it was expected 

 would be the case at Niagara, then nitrate of soda 

 could be made artificially at about £^ per ton. 



Such an electrical process was installed at Niagara 

 by Bradley and Lovejoy, who produced a number of 

 arcs between platinum poles with a continuous current 

 zX a potential of 10,000 volts. The oxides of nitrogen 



