hat will furnish ammonia or nitrogen at the cheapest rate,"
said the Doctor, "is the best to use. The muriate of ammonia contains
the most ammonia, but the sulphate, in proportion to the ammonia, is
cheaper than the muriate, and far cheaper than the carbonate."

Carbonate of ammonia contains 21-1/2 per cent of ammonia.

Sulphate of ammonia contains 25-3/4 per cent of ammonia = 21-1/5 of
nitrogen.

Muriate of ammonia contains 31 per cent of ammonia = 25-1/2 of nitrogen.

Nitrate of soda contains 16-2/5 per cent of nitrogen.

Nitrate of potash, 13-3/4 per cent of nitrogen.

From these figures you can ascertain, when you know the price of each,
which is the cheapest source of nitrogen.

"True," said I, "but it must be understood that these figures represent
the composition of a pure article. The commercial sulphate of ammonia,
and nitrate of soda, would usually contain 10 per cent of impurities.
Lawes and Gilbert, who have certainly had much experience, and doubtless
get the best commercial articles, state that a mixture of equal parts
sulphate and muriate of ammonia contains about 25 per cent of ammonia.
According to the figures given by the Doctor, the mixture would contain,
if pure, over 28 per cent of ammonia. In other words, 90 lbs. of the
pure article contains as much as 100 lbs. of the commercial article."

As to whether it is better, when you can buy nitrogen at the same price
in nitrate of soda as you can in sulphate of ammonia, to use the one or
the other will depend on circumstances. The nitrogen exists as nitric
acid in the nitrate of soda, and as ammonia in the sulphate of ammonia.
But there are good reasons to believe that before ammonia is used by the
plants it is converted into nitric acid. If, therefore, we could apply
the nitrate just where it is wanted by the growing crop, and when there
is rain enough to thoroughly distribute it through the soil to the depth
of six or eight inches, there can be little doubt that the nitrate, in
proportion to the nitrogen, would have a quicker and better effect than
the sulphate of ammonia.

"There is another point to be considered," said the Doctor. "Nitric acid
is much more easily washed out of the soil than ammonia. More or less of
the ammonia enters into chemical combination with portions of the soil,
and may be retained for months or years."

When we use nitrate of soda, we run the risk of losing more or less of
it from leaching, while if we use ammonia, w