Chemical analysis defines only the composition of a
manure. In determining the commercial value, we have to
inquire concerning the origin of its constituents — that is, we
must find whether the phosphates are from bone or from a
mineral source, and if the nitrogen exists as a soluble
ammonia salt or is derived from nitrogenous matter. These
are necessary inquiries, for bone phosphates have a higher
agricultural value than mineral phosphates of equal strength,
and the nitrogen of sulphate of ammonia is worth consider-
ably more than the same element, derived from treated leather
waste or dried blood. Superphosphates are bought on the
amount of soluble phosphate they contain. By this is under-
stood not the actual amount of mono-calcic phosphate which



BONE PRODUCTS AND MANURES 127

is the soluble part of the manure, but its equivalent as
tribasic phosphate of lime made soluble by acid treatment.
All phosphates, ammonias, and potashes, are now bought
at a fixed price per unit. This price naturally varies
according to its manufactured or raw state. For instance, a
mineral phosphate may be bought at 8d. per unit — that is,
8d. for every percentage of tribasic phosphate present ; when
treated with acid and rendered soluble, the same unit of
tribasic phosphate has a value of Is. 6d. or Is. 8d., according
to the price ruling. Then, again, the value of the unit of
amraonia from sulphate of ammonia may be 15s., and the
unit from nitrogenous matter worth only 8s.
