son, and deficient at its end. In order
to dissolve bones, bone ash, or mineral phosphates, they are mixed with
from a third to half their weight of sulphuric acid, of specific gravity
1.70 or 140 deg. Twaddell. When mineral phosphates, and particularly
coprolites, are used, the quantity of sulphuric acid must be increased
so as to compensate for the loss of that which is consumed in
decomposing the carbonate of lime they contain. When operating on the
small scale, the materials are put into a vessel of wood, stone, or lead
(iron is to be avoided, as it is rapidly corroded by the acid), and
mixed with from a sixth to a fourth of their weight of water, which may
with advantage be used hot. The sulphuric acid is then added, and mixed
as uniformly as possible with the bones. Considerable effervescence
takes place, and the mass becomes extremely hot. At the end of two or
three days it is turned over with the spade, and after standing for some
days longer, generally becomes pretty dry. Should it still be too moist
to be sown, it must be again turned over, and mixed with some dry
substance to absorb the moisture. For this purpose everything containing
lime or its carbonate must be carefully avoided, as they bring back the
phosphates into the insoluble state, and undo what the sulphuric acid
has done. Peat, saw-dust, sand, decaying leaves, or similar substances,
will answer the purpose, and they should all be made thoroughly dry
before being used. An excellent plan is to sift the bones before
dissolving, to apply the acid to the coarser part, and afterwards to mix
in the fine dust which has passed through the sieve, to dry up the mass;
or a small quantity of bone ash, of good quality, or Peruvian guano, may
be used. On the large scale, mechanical arrangements are employed for
mixing the materials, so as to economise labour, and mineral phosphates,
such as apatite, can then be used with advantage. In such cases, blood,
sulphate of ammonia, soot, and other refuse matters, are occasionally
used to supply the requisite quantity of nitrogenous substances, but
large quantities are also made from bone ash, etc., without these
additions.

The composition of superphosphates must necessarily vary to a great
extent, and depends not only on the materials, but on the proportion of
acid used for solution. The following analysis illustrates the
composition of good samples made from different substances--

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