_ 4 



when working with a mixture containing the same proportions of 

 nitrogen and oxygen, and that even at a temperature of 3000 C. only 

 some five per cent of the gases combine. Another fact which renders 

 the process difficult is that the gas must not be kept at this 

 temperature for any length of time, as at such high temperature 

 the nitric oxide is rapidly dissociated ; as a result the conditions 

 to be aimed at are a very rapid heating to a high temperature and a 

 very rapid cooling. In the Birkeland furnace the heating is indeed 

 rapid, but the cooling is by no means so easy to accomplish. 



From what has been said it will, I think, be evident that for the 

 manufacture of electric nitrates, etc., to be successful the supply of 

 power must be large and cheap. I have seen it stated that it is only 

 possible to work profitably if the power costs less than one twenty- 

 fourth of a penny per unit. At the present time quite a large amount 

 of power is being made use of in Norway for the production of nitrates. 

 It is estimated that altogether there are some six million h.p. available 

 in that country. 



Other forms of furnace have been devised of which that of 

 Schonherr is the most widely used ; this is the pattern which has 

 been very largely used by the Badische Anilin Soda Fabrik and 

 has probably played a very important part in the production of ex- 

 plosives for Germany. In this form of apparatus an arc is produced 

 in a long tube and the air is made to travel through the tube and 

 around the arc in a spiral. The arc terminates in a water-cooled 

 chamber in which the gases are rapidly cooled to about 600 C. The 

 arc starts from a massive iron electrode and is so intense that the end 

 is at once melted and the ferric oxide formed is literally boiled away. 

 Comparative trials of this form with Birkeland's show that the 

 Schonherr furnace has the greater efficiency. 



Per K.V.A. hour. 



Birkeland and Eyde 70 grammes HN0 3 2 per cent NO 

 Schonherr 75 M 2-5 



per kilowatt-hour. Several other types of furnace have been devised 

 but are not employed on any large scale. 



It may at first seem strange that so great an amount of power is 

 needed to produce such a comparatively small result. The reason 

 for this is that the chemical combination of nitrogen with oxygen is 

 accompanied by an absorption and not an evolution of heat, as is the 

 case with most of the common chemical reactions with which we are 

 familiar. As a result of this the reaction will at once cease if the supply 

 of energy is cut off. It appears that the action of the arc is purely a 

 thermal one ; that any other method of heating would be equally 

 successful, but the electrical method is the more convenient. On 

 account of the fact that the combination will not take place without a 



