78 . A. W. Stewart on 



increasing one, and it is evident that comparatively a short period 

 may be given as sufficient to exhaust the available supplies. 



There remains one other source of nitrogen, the atmosphere, 

 and the chemical i)roblem is how to convert this nitrogen into 

 compounds which the vegetable world can use as nourishment. 

 This is now actually being done on a very large scale. For the 

 " fixation of atmospheric nitrogen " it is essential to employ 

 energy in some form or other, and, since these compounds have 

 to compete in price with the Chili nitrates, the power must be 

 inexpensive. Water power, favourably situated, is the cheapest 

 form of energy, and thus Norway has many advantages. 



This Norwegian industry was set on foot by Professors 

 Birkeland and Eyde, at Notodden, and in 1913 no less than 

 110,000 tons of nitrogenous material was synthesised by the 

 Birkeland-Eyde works. 



If air be heated strongly some of the nitrogen becomes 

 combined with the oxygen present, the quantity depending upon 

 the temperature. Thus at 2,675° six times as high a proportion 

 is converted as at 1,811", but to keep this proportion the mixture 

 must be very rapidly cooled. If allowed to cool slowly the 

 combination breaks up until the proportion present becomes only 

 that arising from the then temperature. 



The higher the temperature and the quicker the cooling the 

 greater will be the percentage of combined nitrogen. In the 

 Birkeland-Eyde pi-ocess the air is blown through an electric arc, 

 which is spread out by the aid of an electro-magnet into a disc of 

 flame about six feet in diameter, thus allowing the passage of 

 large quantities of air across the disc of flame to a cooling 

 arrangement in which it is very rapidly deprived of its heat. 



In another process the electric furnace is used to produce 

 cyanamide, which is formed when lime and coke are heated in 

 the presence of a stream of nitrogen. This substance comes on 

 the market as a fertiliser under the name of nitrolim. 



In a third process, described by A. K. Macbeth in the 

 jpajjcr already referred to and due to Haber and Le Rossignol, 



