on of the bone-dust be
considered worth before it was converted into superphosphate?"

"A ton of bone-dust," replied the Doctor, "contains 76 lbs. of nitrogen,
worth, at 18 cents per lb., $13.68, and 464 lbs. phosphoric acid, worth
7 cents per lb., $32.48. In other words, a ton of bone-dust, at the
usual estimate, is worth $46.16."

"And," said the Deacon, "after it is converted into superphosphate, the
same ton of bones is worth $72.58. It thus appears that you pay $26.42
per ton for simply making the phosphoric acid in a ton of bones soluble.
Isn't it paying a little too much for the whistle?"

"Possibly such is the case," said I, "and in point of fact, I think
bone-dust, especially from steamed or boiled bones, can be used with
more economy in its natural state than in the form of superphosphate."

Superphosphate can be made more economically from mineral phosphates
than from bones--the nitrogen, if desired, being supplied from
fish-scrap or from some other cheap source of nitrogen.

But for my own use I would prefer to buy a good article of
superphosphate of lime, containing no nitrogen, provided it can be
obtained cheap enough. I would buy the ammoniacal, or nitrogenous manure
separately, and do my own mixing--unless the mixture could be bought at
a less cost than the same weight of soluble phosphoric acid, and
available nitrogen could be obtained separately.

A pure superphosphate--and by pure I mean a superphosphate containing no
nitrogen--can be drilled in with the seed without injury, but I should
be a little afraid of drilling in some of the ammoniacal or nitrogenous
superphosphates with small seeds.

And then, again, the "nitrogen" in a superphosphate mixture may be in
the form of nitric acid, or sulphate of ammonia, in one case, or, in
another case, in the form of hair, woollen rags, hide, or leather. It is
far more valuable as nitric acid or ammonia, because it will act
quicker, and if I wanted hair, woollen rags, horn-shavings, etc.,
I would prefer to have them separate from the superphosphate.

CHAPTER XXXVIII.

SPECIAL MANURES.

Twenty five to thirty years ago, much was said in regard to special
manures. Fertilizers were prepared for the different crops with special
reference to the composition of the plants.

"But it was known then, as now," said the Doctor, "that all our
agricultural plants were composed of the same elements."

"True, but what was claimed was this: Some crops cont