sulphuric
acid. As Dr Aitken has pointed out, the germ life in the soil and in the
bones gradually converts them into a form available for the nourishment
of plants; but to dissolve bones with sulphuric acid is to kill out the
germ life and retard the decay of any nucleus of bone in the dissolved
manure.

_Dissolved Bones._

Dissolved bones, however, are still manufactured. Formerly the manure
called dissolved bones was often a mixture of mineral superphosphate
along with undissolved bone-meal, but recent legislation has stopped the
continuance of this practice. The composition of dissolved bones varies
somewhat, the percentage of soluble phosphate being about 20 to 23 per
cent, the insoluble amounting to from 9 to 10 per cent, and the nitrogen
from 2-1/2 to 3-1/2 per cent.[218] Another reason against dissolving
bones is to be found in the difficulty experienced in dissolving their
phosphate. Bones, especially when raw, are not easily acted upon by
acids.

_Crops suited for Bones._

Bones are commonly regarded as being specially beneficial to
pasture-land, to which they are applied as a top-dressing. Turnips,
tobacco, potatoes, vines, and hops are also much benefited by the
application of bones. In America, mixed with wood-ashes (the chief
manurial constituent of which is potash), they have been extensively
used as a substitute for farmyard manure, and have been applied at the
rate of 5 to 6 cwt. per acre. In Saxony, according to Professor Storer,
1 cwt. of fine bone-meal is worth as much as 25 to 30 cwt. of farmyard
manure.

_Bone-ash._

The ash which is left on burning bones used to be an article of
considerable manurial importance. It is still imported from South
America in some quantity, and is used chiefly in the pottery industry.
It is occasionally still used to a limited extent for the manufacture of
high-class superphosphates. It is extremely rich in phosphate of lime,
of which it contains between 70 and 80 per cent; but of course it is
devoid of nitrogen.[219] Bone-ash is best used in the dissolved form, as
it possesses no characteristic action such as is possessed by bones.

_Bone-char or Bone-black._

When heated in a closed retort, bones are not converted into bone-ash,
but into a body called bone-char. This body is similar in composition to
bone-ash, except for a certain percentage of charcoal--amounting, on an
average, to 10 per cent. It contains but little nitrogen and other
organic ma