Germany 19 35
Belgium 30 35
France 17 20
United Kingdom 28 32
United States 12 15

The greatest gain was made in Germany and we see a reason for it in the
fact that the German importation of Chilean saltpeter was 55,000 tons in
1880 and 747,000 tons in 1913. In potatoes, too, Germany gets twice as
big a crop from the same ground as we do, 223 bushels per acre instead
of our 113 bushels. But the United States uses on the average only 28
pounds of fertilizer per acre, while Europe uses 200.

It is clear that we cannot rely upon Chile, but make nitrates for
ourselves as Germany had to in war time. In the first chapter we
considered the new methods of fixing the free nitrogen from the air. But
the fixation of nitrogen is a new business in this country and our chief
reliance so far has been the coke ovens. When coal is heated in retorts
or ovens for making coke or gas a lot of ammonia comes off with the
other products of decomposition and is caught in the sulfuric acid used
to wash the gas as ammonium sulfate. Our American coke-makers have been
in the habit of letting this escape into the air and consequently we
have been losing some 700,000 tons of ammonium salts every year, enough
to keep our land rich and give us all the explosives we should need. But
now they are reforming and putting in ovens that save the by-products
such as ammonia and coal tar, so in 1916 we got from this source 325,000
tons a year.

[Illustration: Courtesy of _Scientific American_.