THE NITEOGEX PROBLEM. 99 



thus passing" in opposite directions. The gases, before being" 

 finally restored to the atmosphere, are made to pass up a tower 

 down which a weak solution of soda is passed. 



■ The final products obtained in the absorption system are 

 nitric acid of a concentration about 35 per cent., and in the last 

 to'v\er sodium or calcium nitrite and nitrate. Formerly, the 

 nitric acid obtained was neutralised by flowing on to limestone 

 contained in granite vats, a watery solution of calcium nitrate 

 being thus obtained, which was afterwards concentrated in 

 vacuum evaporators to a certain strength and then poured over 

 steam cylinders for final solidification. The salt thus produced 

 was found to be deliquescent and the basic nitrate was then 

 manufactured, but this also was abandoned in favour of the 

 manufacture of concentrated nitric acid. By these means 

 about 95 per cent, of the oxidised nitrogen passed through the 

 system is recovered in practice. The fundamental reactions 

 which take place are : — 



(a) In the flame disc, N", + 0o^=52 NO. 



(b) After cooling- the exit gases, 



2 K'O + Oo 600^- 2 XOa li^- NX)^. 



(c) Absorption by water, 2 NO. + H.O— --HXO. + HNO,. 



(d) Subsequent oxidation, 2 HNO, + 0, = 2 HXO3. 



As shown in the equations, these reactions are reversible, 

 and the dynamics of the process has been studied theoretically 

 with useful results, by passing air into a platinum globe 

 heated to a high temperature in an electric furnace, and after 

 equilibrium had been attained cooling quickly by passing the 

 gases through a capillary tube and then analysing. The 

 concentration of nitric oxide at various temperatures was thus 

 obtained, both by experiment and calculation, as also its rate 

 of formation and decomposition, which afforded valuable data 

 for the conduct of operations on the large scale. By increasing 

 the volume of oxj^gen in the mixture until it was equal to that 

 of the nitrogen, the concentration of the nitric oxide was 

 increased, as also by decreasing^ the rate of flow through tlie' 

 heated globe, but in practice these have not been adopted 

 generally. 



Ih.—The l^chonhrr Process (1907). 



This differs from the above only in the type of furnace 

 used, which consists of a vertical cylinder 23 feet high lined 

 with refractory brick, inside which is an iron tube about 

 five to six inches in diameter containing an insulated electrode 

 at one ^vA, the tube itself serving as the second electrode. 

 Air is introduced into this tube with a tangential or rotary 

 motion, and the arc which is formed between the insulated 

 electrode and the adjacent tube is thus drawn out to a length 

 of six to seven yards. The gases leave at the upper end at a 

 temperature of about 2,000° C, and are cooled by a water 

 jacket placed round the arc tube near the top, and, secondly, 

 by being made to heat the incoming air. The furnace requires 

 about 40,000 to 50,000 cubic feet of air per hour, and is 



