MINERAL INDUSTRIES OF THE UNITED STATES — FERTILIZERS. 13 
iron and steel industry. At first the coke was made without regard 
to saving the volatile portion, the process being carried out in the 
so-called beehive ovens, which not only waste valuable constituents 
of the coal but actually consume a considerable part of the coal itself. 
To say that this method should never have been utilized, or should 
now be stopped by drastic means, would be to overlook the fact that 
progress in such matters can scarcely exceed the industrial demands 
for the products involved. This country is just now in a transitional 
state in this respect ; an increasing amount of coal is being made into 
coke in a modern type of oven, known as the retort or by-product 
oven, which not only produces a maximum of coke but at the same 
time yields gas, nitrogen in the form of ammonia , 1 and coal tar, this 
last convertible into dyes, medicinal preparations, explosives, and 
other compounds. Thus the production of nitrogen from coal is 
closely dependent upon the production of its associated by-products, 
and is limited at any given time by the demand for coke on the part 
of the iron industry and the demand for other coal products on the 
part of other industries. The proper development of coal-product 
nitrogen must, therefore, go hand in hand with a well-balanced 
growth of the entire coal-products industry; and to reach its full 
fruition, must expand beyond the limits imposed by the needs for 
metallurgical coke through a gradual extension of the uses of coke to 
fuel and power purposes. 
But coal-product nitrogen, while the most promising partly devel- 
oped source of nitrogen in this country to-day and open to consider- 
able and somewhat rapid expansion, must nevertheless remain a 
transient source, if transient be interpreted to represent a few cen- 
turies. The ultimate source, it would seem, upon which the world 
must eventually depend is the atmosphere. Coal-product nitrogen, 
indeed, on the last analysis, is merely atmospheric nitrogen rendered 
more readily available by geological processes of past ages, and is 
therefore a tide-over from a purely mineral source to the atmosphere. 
The world, in fact, is already turning to the atmosphere for a sig- 
nificant part of its nitrogen. Three processes for securing nitrogen 
from the air have proved successful under different circumstances, 
and other processes are in the course of experimentation, if not actual 
development. The three processes which have proved practicable 
under certain limitations are the arc process, the cyanamid process, 
and the Haber process. 
The arc process produces nitric acid by means of the combustion of 
nitrogen and oxygen in the electric arc. It requires large quantities 
of cheap electric power and has proved successful in Norway, where 
1 About a third of this ammonia is used in refrigeration, some 10 per cent in 
the manufacture of explosives and chemicals, while half or more goes into fer- 
tilizers in the form of ammonium sulphate. 
