416 SECTIONAL COMMUNICATIONS. 



The arc process, the oldest method of obtaining fixed nitrogen from 

 the air, consists in bui'ning air by passing it quickly through an intensely 

 hot electric flame. In the best known type of furnace, the Birkeland- 

 Eyde, this flame is a powerful arc, spread out by a magnetic field into 

 a sort of Catherine-wheel, several yards in diameter. A small per- 

 centage of the nitrogen and oxygen traversing the path of the arc is 

 caused to combine, and the resulting nitric oxide is ultimately further 

 oxidised to nitric acid or nitrates. This process was commercially 

 operated in Norway in 1904, and in the hands of the original company 

 it has been uniformly successful, and has reached an enormous develop- 

 ment. Although the power requirements are very large, it affords the 

 cheapest known method for the manufacture of nitric acid. It has not 

 been sufficiently recognised that the arc process owes its initiation to 

 scientific researches carried oat mainly by British investigators. During 

 the War the officials of the Norsk Hydro Company told me that Prof. 

 Birkeland used to recognise frankly that his inspiration was derived 

 from the famous British Association address of Sir "William Crookes, 

 and especially from the quantitative experimental work of the late Lord 

 Eayleigh, whose big flask mounted on a wooden stool at the Eoyal 

 Institution, and provided with a pair of metal poles and an internal 

 potash fountain, is the lineal ancestor of all the great Norwegian plants 

 of to-day. These experiments, employing one or two horse-power, in 

 which Lord Eayleigh carefully measured for the first time the relation 

 between the energy consumed and the amount of nitrogen fixed, pointed 

 the road to all that has since happened in Norway. At Notodden plant 

 is now installed to utilise about 45,000 kw., and in the two great works 

 at Ejukan I saw furnaces in operation employing in all over 200,000 kw., 

 or 270,000 continuous horse-power, this energy being generated at what 

 is almost certainly the cheapest hydro-electric plant in the world. At 

 Ejukan II. a 15,000 kw. steam-operated set has been added to utilise 

 waste steam raised in the boilers employed in the cooling of the process 

 gases, which leave the furnace at about 1,000° C. During the later war 

 period almost the whole output of these enormous works came to 

 England and France for munition purposes. 



It is, however, startling to remember that less than 2 per cent. 

 of the electrical or heat energy expended in the average arc furnace is 

 absorbed as chemical energy in the initial oxidation of the nitrogen. 

 The concentration of nitric oxide in the gases leaving the furnace 

 averages only about 1.2 per cent., and many suggestions have been 

 made for improving the efficiency. About fourteen arc plants of various 

 types, mostly of small output, are now distributed throughout the world. 

 Among these I may mention an experimental plant of about 300 kw. 

 capacity which was erected at a munition works at Birmingham on 

 the Kill) urn Scott system. 



Enriched air has been used on a considerable scale by a company 

 operating works in Switzerland and Germany. The oxygen content 

 of the air is increased to 50 per cent., and the whole operatiori is carried 

 out in a closed circuit. The product is generally removed as liquid 

 nitrogen peroxide by cooling, instead of being absorbed in towers. 

 Although the ino'ease in yield was considerable, certain serious diffi- 



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