/I 
must always be quite insufficient to meet the demand" of the agri- 
culturists. 
The main supply of Nitrogen for fertilization is at present 
chiefly obtained from natural deposits of Nitrates which occur in 
certain countries. With respect to this source of plant nitrogen 
also, the available quantity is limited and in view of the enormous 
extension of cultivated areas demanding scientific fertilization, 
the day is not distant when the output of this fertilizer will de- 
crease and will ultimately become exhausted. Of these fertilizers 
the two best known are the nitrates of Potash and Soda. Both 
of these are found in considerable natural deposits, the former 
in India and Persia, and the latter in Chili. Nitrate of Soda, is 
known as Chili Saltpeter, and is used very extensively in agri- 
culture. It is also largely used in the manufacture of Nitric 
Acid and of other chemicals, for as has been said, the extreme 
inertness of the free gas Nitrogen, has caused the naturally ex- 
isting supply of the world's nitrates to be resorted to for the 
formation of many new nitrogenous combinations. In this way 
the available deposits are being rapidly exhausted and in order 
to insure the continued prosperity of many agricultural crops, it 
is imperative that a new supply of nitrates be forthcoming. 
Where then, when the natural deposits have disappeared, will 
agriculturists turn for their new supply of nitrogen fertilizers? 
The most ready means of satisfying this demand which sug- 
gests itself, is to tap the great air reservoir of its Nitrogen, and 
then to discover some way of combining it chemically with suit- 
able substances. 
The atmosphere may be described as a aerial ocean surround- 
ing the earth. From the time of Aristotle until less than one 
hundred and fifty years ago it was regarded as one of the four 
elements. It is now known to consist almost entirelv of a me- 
chanical mixture of the two gases Nitrogen and Oxygen, in 
the proportion of about four volumes of the former to one of the 
latter. A graphic representation of this proportion may be had 
by inscribing a circle within a square. In such a figure the 
circle will represent the Nitrogen present in the atmosphere and 
the four spaces at the corners of the square, the Oxygen. 
Besides the Nitrogen contained in the atmosphere in mechanical 
mixture with Oxygen, there are also present traces of Nitrogen 
in chemical mixture with Hydrogen, and also with Hydrogen 
and Oxygen together. Of these latter compounds Ammonia 
(N H 3 ) and Nitric Acid (H. N. O s ) are the most important to 
plant life, but they occur in infinitesimal amounts, varying ac- 
cordingly to local and meteorological conditions. 
The presence of Ammonia in the atmosphere is chiefly due to 
the decomposition of organic matter. The precipitation of rain 
brings with it small quantities of this compound which is thus 
rendered available for plant use. The occurrence of electrical 
disturbances in the air produces Nitric Acid and in India, where 
