THE UTILISATION OF THE NITROGEN OF THE AIR. 185 
believed, however, that within the last two years the problem has 
been successfully solved by two totally distinct methods. In the 
first of these, which has been worked out by two Norwegian 
scientists, Professor Birkeland of Christiania University and 
Mr S. A. M. Eyde, a Norwegian engineer, the reaction which 
has been made use of is the combination of the oxygen and 
nitrogen of the air under the influence of the electric spark, first 
discovered by Cavendish. Briefly the process consists in 
passing a current of air through a powerful electric arc flame of 
special construction, whereby combination between the oxygen 
and nitrogen takes place. The fumes of oxides of nitrogen, 
as the compounds formed are termed, are absorbed in towers 
filled with limestone and afterwards worked up into “Lime 
Nitrate,” the name the product has received commercially. 
After many trials on a small scale, works for carrying out this 
process were erected at Notodden, in Norway, in May 1905, and 
so successful has the process been, that large extensions are now 
in progress, and it is expected that an installation of 30,000 horse- 
power will soon be in full operation. The annual output of the fully 
extended works is estimated at 20,000 tons. The basic calcium 
nitrate, or “lime nitrate,” as it is called, contains about 132 per 
cent. of nitrogen, and can be obtained in the form of a fine dry 
powder which can be readily distributed by an ordinary sowing- 
machine. Precise details as to cost are not yet available, but it is 
expected that the new fertiliser will compete in price with nitrate of 
soda. Considering how essential the supply of electric energy 
at a low price is for the success of the process, it is perhaps 
inevitable that the works should have been started in some 
country like Norway, where cheap water-power is so abundant. 
So far as it has been tested, lime nitrate seems to be quite equal 
to Chili saltpetre as a fertiliser. 
The second method is quite different in principle from the one 
described above, and has been patented by two German 
chemists, Drs Frank and Caro. Its starting-point is the well- 
known substance calcium carbide, now so largely employed for 
generating acetylene gas for lighting purposes. This substance 
is prepared by heating together in an electric furnace, to a high 
temperature, calcium carbonate, or chalk, and coke or some 
other convenient form of carbon. Nitrogen gas is next prepared 
by passing air through a cylinder containing metallic copper, 
heated up to a suitable temperature, whereby the oxygen of the 
VOL. XX. PART II. N 
