XXXVI ROYAL SOCIETY OF CANADA 
Central Experimental Farm have shown that a single crop of clover 
ploughed under improves subsequent crops for several years. In the 
tests made with oats the average increase in crop has been about ten 
bushels per acre of grain with a considerable increase in the weight of 
straw. Barley which followed the oats without any further ploughing 
under of clover, has given an increase in grain almost equal to that of 
the oats, with a lesser increase in straw, while a third crop on the same 
land has shown a decided, although reduced, increase. 
Nitrogen is the most expensive constituent of artificial fertilisers, 
at the same time it is indispensable. It produces a strong and healthy 
growth of foliage, and helps to build up the so-called plant albuminoids, 
which are so nourishing to animal life. Nitrogen is now supplied to 
the soil artificially in the form of sulphate of ammonia and nitrate of 
soda, both soluble nitrogenous salts. 
The sulphate of ammonia is a by-product formed in connection with 
the manufacture of illuminating gas. Formerly this was wasted, but 
now almost every large gas works has its sulphate of ammonia plant, 
and the total annual production of this salt is estimated at nearly 
500,000 tons, more than one-half of which is used in the manufacture 
of fertilisers. 
Nitrate of soda, however, is the principal source of the nitrogen 
provided in artificial fertilisers. This salt occurs in enormous deposits 
in the northern parts of Chili, principally in the Province of Tarapaca. 
It is found in layers varying in thickness from a few inches to ten or 
twelve feet, lying usually on a deposit of clay and gravel, near the sur- 
face and beneath a covering of sand and gypsum. The impure salt is 
dug out or blasted, and purified by dissolving in water and crystallising. 
The nitrate of soda industry has developed enormously in recent years. 
In 1884, the total output was 550,000 tons, in 1900 it was 1,490,000 
tons. It is held by those who have carefully examined these deposits, 
that at the present rate of mining they will be exhausted within twenty- 
five years, in which case there will be a serious deficiency in nitrogen 
for fertilising unless a new source of supply should meanwhile be 
discovered. 
With a nitrogen famine in prospect many attempts have been made 
to utilize directly the nitrogen in the air and bring it into such a state 
of combination as will make it available for agricultural purposes. The 
advantages which would result from the obtaining of nitrogen compounds 
at a reasonable cost from this inexhaustible source can scarcely be over- 
estimated. 
Some three or four years ago a new nitrogenous fertiliser was pro- 
duced in Germany, known as calcium cyanamide, or lime nitrogen. 
