II.] ELECTRICAL FIXATION OF NITROGEN 43 



generated were converted into nitric and nitrous acids 

 by steam and more oxygen, and a mixture of sodium 

 nitrite and nitrate was prepared for agricultural pur- 

 poses. The installation, however, only ran for fifteen 

 months, for though considerable amounts of nitric 

 acid were produced, technical difficulties in maintaining 

 the apparatus in working order proved insuperable. 

 More recently a working process has been devised by 

 Berkeland and is running on a commercial scale at 

 Notodden in Norway. In the Berkeland-Eyde process 

 an alternating current at about 5000 volts is set to form 

 an arc between U-shaped copper electrodes, which are 

 hollow and kept cool by a current of water within. 

 The electrodes are placed equatorially between the 

 poles of a powerful electro-magnet, which has the 

 effect of causing the arc to spread out into a broad 

 flat flame. Though the temperature of the arc-flame 

 is calculated to be 2600° C, it is not particularly 

 luminous; it may be looked at directly from a yard's 

 distance. 



Through the furnace in which this special arc is 

 generated about 15,000 litres of air are blown per 

 minute at gentle pressure and the issuing air contains 

 about I per cent, of nitric oxide and is at a temperature 

 of 600° to 700° C. It is cooled and then passes into 

 two oxidising chambers, where the combination of the 

 nitric oxide with the oxygen of the uncombined air 

 takes place, after which it passes into a series of five 

 condensing towers. Down the fourth tower, which 

 is filled with broken quartz, water trickles and picks 

 up enough of the nitrous gases to become 5 per 

 cent, nitric acid at the bottom ; this is pumped up 

 and trickles down the third tower, the process being 

 repeated until the liquid leaving the bottom of the 

 first tower contains 50 per cent, of nitric acid. In the 



