98 THE XITEOGEX TEOBLEM. 



6. Conversion into the oxides of nitrogen by tlie explosion 

 of a combustible gas with air, and absorption of these gases by 

 water as in the first process. This is known as the Hiiusser. or 

 explosion, process, and has been worked on a small scale with 

 some success, using coke oven gas with air and exploding the 

 mixture in stationary bombs. If employed as a method of 

 producing power as well as nitric acid, the cost of the latter 

 would compare more than favourably with the products 

 obtained by the synthetic processes mentioned before, and the 

 scheme is therefore one which invites further experiment, in 

 spite of the great cost of the absorption plant which would be 

 required for the very low concentration of nitric oxides 

 obtained. 



In addition to these, a large number of other processes 

 have been proposed, but serious attempts have not l)een made 

 to work them out commercially, and they are therefore for the 

 moment, so to speak, of academic interest only. The case is 

 otherwise with those specificallj' mentioned above, since the 

 first three processes are, commercially speaking, large pro- 

 ducers; and with regard to the last three, small plants are in 

 operation with a view to overcoming the difficulties incident to 

 large-scale production at a later stage. A brief account of the 

 methods used in the above processes, the character aiid amounts 

 of the products obtained and the factors needful for their 

 successful operation may not be considered out of place here. 



1 a.— The Birlehind-Ej/de Process (1903). 



This has the merit of being the first nitrogen fixation 

 process to meet with commercial success, having been intro- 

 duced in 1903, when large works were first erected at IVotoddeu, 

 in Norway, power being transmitted at 10.000 volts from the 

 Svaelgfos Power Station, three miles away, on the Tyn River, 

 where there is an effective height of fall of about 140 feet. Air 

 is driven at the rate of approximately 2 cubic metres (TO cubic 

 feet) per minute through a flame disc at a temperature of 

 2.000° C. to 3.000° C. produced by electro-magnetic deviations 

 of an electric arc. The electrode^ are made of thick copper 

 tubing and are water cooled. The diameter of the flame disc 

 is between two and three yards. By this meaJis a product is 

 obtained containing about Ih per cent, of nitric oxide. The 

 gases leave the furnace at a temperature of 800° to 1,000° C. 

 and are passed into boilers where the temjierature is reduced to 

 150° to 200° C, the heat being utilised to raise steam, to con- 

 centrate the final products, and for other purposes. They next 

 pass to the coolers, which consist of aluminium tubes cooled 

 externally by cold flowing water, and tlience to the oxidation 

 tanks, vrhich consist of vertical iron cylinders lined with acid- 

 proof stone. Here the nitric oxide combines with the 

 unconverted oxygen to form the peroxide. The cooled gases 

 are then forced through a series of granite absorption towers, 

 in which the peroxide is dissolved out by means of water, which 

 is used in the last tower but one of the series, the weak nitric 

 acid produced being then pumped to the top of the next tower 

 nearer the oxidation tanks, and so on. the gas and the solvent 



