354 
This process consists briefly of driving a current of aii through 
a chamber in which it comes in contact with an electric arc situ- 
ated in a magnetic field. The electrodes are fork shaped, water 
cooled, and are set perpendicular to the lines of magnetic force 
so that the discharges form a disk of sparks. When once set 
these arcs burn weeks without regulation and the electrodes last 
for months. There is a limiting value, however, to the forma- 
tion of nitric oxide, about 5%, and at the higher temperatures 
at which the oxidation takes place the action is reversible. It 
will be seen then that the important point in working the 
furnaces is to have the reaction take place at the highest tem- 
perature of the arc in order to get a high yield of nitric oxide 
and then to quickly cool the gas so that the reverse action does 
not take place. This has been accomplished in practice by sweep- 
ing the gas out of the region of the arc so as to be instantly 
cooled by the surrounding air, and by electrical and mechanical 
means whereby the arcs are interrupted several thousand times 
a second. 
The waste heat from the treated air is used under the boilers 
for evaporating and concentrating purposes, and is then con- 
ducted to oxidation tanks where the NO is gradually changed to 
nitrogen peroxide as soon as the temperature falls below 600° C. 
by the excess oxygen always present. The gases then enter ab- 
sorption towers filled with broken quartz or acid proof stones 
and down which dilute nitric acid slowly runs. When the acid 
reaches the proper concentration it is drawn for shipment or 
for the treating of either soda or lime to form nitrates. The 
oxides of nitrogen which escape the absorption towers are car- 
ried up a wooden tower in which they meet a fine spray of soda 
solution and are fixed as a weak solution of sodium nitrate and 
nitrite. From the nitric acid nitrate of soda, nitrate of potash, 
nitrate of lime, or ammonium nitrate may be formed. As a good 
quality of limestone is found near Notodden, where the Birke- 
land-Eyde system is installed and, as soda would have to be im- 
ported for manufacturing sodium nitrate, nitrate of lime has 
been the finished product. The limestone is treated with weak 
nitric acid and a dilute solution of nitrate of lime formed which 
is concentrated, crystalized and ground. It is then packed in 
tight barrels of about 220 pounds. 
In 1909 the Notodden works produced 12,600 tons nitrate of 
lime, 2700 tons nitrate of soda, and 370 tons of sodium nitrate 
and nitric mixed. The markets of Europe have absorbed this 
output and will probably continue to do so to a greater or less 
extent for some time to come. The combustion of atmospheric 
nitrogen has passed out of the experimental stage and today is a 
thriving infant industry. It is simply a matter of time until 
nitrate of lime is as well known to the commercial and agri- 
cultural world as nitrate of soda. 
