38 FERTILISERS CONTAINING NITROGEN [chap. 



result by solution in water ; secondly, nitrogen will 

 combine with a few metals and allied bodies, again at 

 high temperatures, to yield substances which under the 

 action of water give rise to ammonia. It is this latter 

 method which was first developed on a commercial 

 scale by Frank and Caro in Berlin. They did not 

 exactly start with a metal, but with calcium carbide, 

 the substance now so well known as the source of 

 acetylene for illumination. This body, Frank and 

 Caro found, would combine readily with nitrogen gas 

 at quite moderate temperatures, and the resulting sub- 

 stance, calcium cyanamide, nitrolim, or kalk-stickstoff, 

 as it is called, will decompose under the action of water, 

 yielding its nitrogen as ammonia and the calcium and 

 carbon as calcium carbonate. An Italian company, 

 which was the first to take up the patents for the 

 manufacture of calcium cyanamide, has established its 

 factory alongside one of the great producers of calcium 

 carbide at Piano d'Orte in the hills above Rome, where 

 water-power can be obtained for the cheap generation 

 of electricity, and other works are being erected in 

 Norway, in Savoy, and in America, where suitable 

 water-power can be obtained. On theoretical grounds, 

 one electrical horse-power per annum should bring 

 about the fixation of 772 kilogrammes of nitrogen ; in 

 practice 300 to 330 have been attained. In the manu- 

 facturing process the calcium carbide is first roughly 

 ground and then heated in iron tubes through which a 

 current of nitrogen gas is passed. The calcium carbide, 

 which itself results from the reaction of a mixture of 

 chalk and coke in the electric furnace, must either be 

 purchased or manufactured by a preliminary process. 

 The two reactions of forming the carbide and uniting 

 it with nitrogen can indeed be carried out simultaneously, 

 but this method has been abandoned in practice. The 



