3 



shown the way in which the nitrogen of the air could be rendered 

 useful. 



With the invention of the dynamo, powerful electric currents soon 

 became available, and it was not many years before numerous patents 

 were taken out for the production of nitric acid and nitrates from the 

 air by electrical means. All these, however, proved too costly and 

 were never commercially successful, if indeed they ever passed the 

 purely experimental stage. 



In 1890 Sir W. Crookes exhibited a " flaming arc " produced by 

 a current of very high voltage and showed that the flame was really 

 due to the combination of the gases of the atmosphere forming nitric 

 oxide. A few years later Lord Rayleigh made iise of this method in 

 his work on Argon, that remarkable discovery which so wonderfully 

 confirmed the early observation of Cavendish. Lord Rayleigh made 

 many attempts to improve the efficiency of his apparatus and even on 

 a small scale achieved a considerable measure of success. He found 

 that a kilowatt hour would produce fifty grammes of nitric acid. 

 With continuous working this works out to 360 kilos, per kilowatt year. 

 The most efficient modern plant gives about 600 kilos, per kilowatt 

 year. 



In 1902 a company was started to make use of some of the power 

 from the Niagara Power Station for the production of nitrate, but the 

 method employed was not efficient, the plant was very costly, and the 

 scheme failed. The credit of producing the first really practical 

 plant belongs to Prof. Birkeland and Eyde. They erected the first 

 large works at Notodden, where the power of three waterfalls was 

 brought into play, the h.p. developed being about 70,000. The 

 apparatus invented by Birkeland for the electrical treatment of the air 

 consisted of a disc-shaped furnace lined with firebrick in which the 

 electric arc was produced. Birkeland had observed that when an arc 

 produced from an alternating current was acted upon by a powerful 

 magnet it was thrown into a flat disc. Such an arc is produced 

 in the disc-shaped chamber of the furnace and a powerful current of 

 air is driven through it, entering the furnace through the centre and 

 being drawn off at the circumference. The current employed in the 

 Notodden works is alternating at 5,000 volts, and each of the older 

 furnaces took same 800 K.V.A., the disc of flame in these latter being 

 about three metres in diameter. (Furnaces have more recently been 

 constructed which absorb 4.000 K.V.A.) By rapid cooling of the out- 

 going air the oxide of nitrogen is saved from decomposition and the 

 gases are then treated in suitable washing towers with the production 

 of nitric acid, and nitrates of lime and soda. 



Numerous experiments have shown that the degree of combination 

 taking place is dependent entirely on the temperature, that is, of course, 



