314 AGRICULTURAL, ANALYSIS 



In 1903 an improvement in . the manufacture of nitric acid 

 from the atmosphere was made by Birkeland and Eyde. Birke- 

 land employed a continuous current produced by 40 amperes at 

 600 volts, which, in connection with other principles of the method, 

 produced a magnetic field of very great intensity. This led to the 

 invention and establishment of the apparatus which has been 

 erected at Notodden, Norway. The furnaces now constructed com- 

 prise three of identical structure. The energy of the furnace has 

 been carried from 500 to 700 kilowatts, that is from 700 to 1000 

 horse power, for each of them. It has been possible, in the very 

 latest experiments to increase the energy of these furnaces to 1500 

 horse power. It is found, however, that the furnaces work more ef- 

 fectually and give better results at a uniform utilization of from 

 500 to 600 kilowatts. The electric energy necessary for the work- 

 ing of the factory at Notodden is furnished at a price of 32 francs 

 per kilowatt-year. The electricity is furnished by a generator 

 of two thousand kilowatts capacity of a triphase construction and 

 at a tension of 5000 volts. The air sent into the furnace by the 

 ventilators is used up at the rate of 25,000 liters per minute for 

 each one, that is for the three furnaces 75,000 liters per minute. It 

 at once reaches the magnetic field formed by the wall of the fur- 

 nace made of fire clay. The air mixed with the nitric gas pro- 

 duced in the furnace leaves the apparatus through a tube kept 

 at a temperature of from 500 to 700, a temperature much 

 higher than that in other apparatus destined to produce nitric acid. 

 The gases pass first through a tubular boiler where they are cooled 

 to about 200. The steam which is produced in this boiler 

 is utilized in the concentration of the solutions of nitrate of lime 

 which are finally formed. From this boiler the gases are intro- 

 duced into the cooling apparatus which rapidly reduces their tem- 

 perature to 50 or 60, a temperature which is the most 

 favorable to the reactions which result in the formation of nitrous 

 acid. In the magnetic field of the furnace it should be under- 

 stood that there is formed only a single nitrogen combination ; 

 namely, oxid of nitrogen NO. Its proportion reaches about 

 five per cent, of the total volume of gas. At a very high tempera- 

 ture of from 2000 to 2500 the elements of this oxid are separa- 



