THE NITROGEN QUESTION—MUNROE. 935 
in length, produced by an alternating current, is maintained con- 
stantly, the energy required being about 600 horsepower and the 
alternations being 50 per second. Air, which has been heated to 
500° C. by the hot discharge of gases, is blown tangentially into this 
tube so that it surrounds the arc spirally in its passage through the 
tube. This prevents the deflection of the arc, permits of the maxi- 
mum exposure of the air to the heat from the arc, and promptly 
sweeps the heated and reacting air to the cooler portion of the tube 
and beyond. A 2,000 horsepower plant of this character has been in 
operation at Christiansand, Norway, since the autumn of 1907, and 
its success has been such that the building of a 120,000 horsepower 
plant of this character has been undertaken at Rukwan Falls, Nor- 
way. The advantage claimed for this process is that it gives a good 
yield of concentrated gas. 
The third method for the fixation of atmospheric nitrogen referred 
to above has been brought to a successful realization by Frank and 
Caro in their production of calcium cyanamid mixed with carbon or 
“lime nitrogen,” or “ nitrolim,” as it is more recently called. This 
is produced by heating calcium carbide in vertical iron retorts in 
an atmosphere of nitrogen, when the calcium cyanamid, mixed with 
carbon, is formed according to the following equation : 
CaC,+N,— CaCN,+C. 
The nitrogen is obtained by liquefying the air and separating its 
constituents by fractional distillation, or by passing the air over 
heated copper, by which the oxygen is removed from it and the nitro- 
gen separated. A plant with a capacity of nearly 4,000 tons per 
year was started at Piano d’ Orta, Italy, in 1906, and with such sue- 
cess that the production was carried in 1908 to over 40,000 tons per 
annum in five plants, with others building. The material as pro- 
duced is used directly as a fertilizer, but it is a simple matter to 
obtain ammonia from it and by a contact process this may be directly 
converted into nitric acid. 
Yet another indirect source of supply of nitric acid and, there- 
fore, of saltpeter is found in the manufacture of coke, for an im- 
portant product of the by-product coke industry is ammonia, which 
is obtained usually nowadays as ammonium sulphate. I have else- 
where shown?” that 15,773 tons of ammonium sulphate were pro- 
duced in this country in 1905. But as only 3,317,585 tons of the 
37,376,251 tons of coal coked in the census year were coked in by- 
product ovens it was possible, had all been so treated, to have ob- 
%Report on Calcium Cyanamid, Charles E. Munroe, Washington, April 27, 
1907. 
>Bulletin No. 65, Census of Manufactures, 1905, Coke, p. 18, by Charles EB. 
Munroe. 
