ones
were fermented before being used, in order to render their action more
speedy when applied to the soil; and this practice still obtains to the
present day in some parts of the country among farmers. This
fermentation was often effected simply by mixing the bones with water,
and allowing the heap to lie for a week or two. In other cases the bones
were mixed with urine or other refuse matter. The most important step,
however, in the history of the treatment of bones for manure was the
discovery in 1840, by Liebig, of the action of sulphuric acid on them--a
discovery which led to the institution of the manufacture of
superphosphate of lime by Sir John Lawes. The nature of this action will
be explained in the following chapter, so that we need only say here
that the efficacy of the manure by treatment with sulphuric acid is more
than doubled. Bones have thus been used, and still are used, in a
variety of conditions, such as in the raw or green state, bruised,
boiled, steamed, fermented, burned, dissolved, and broken or ground into
various states of fineness, to which the names of 1/2-inch, 1/4-inch
bones, bone-meal, bone-dust, and floated bones are given. We shall now
proceed to discuss the composition of bones, and investigate more
exactly the nature of their action.

_Composition of Bones._

The composition of bone-tissue varies considerably, and depends on the
age and kind of animal to which it belongs, as well as to the part of
the animal frame from which it is taken. Bones are made up of an organic
and an inorganic part. By steeping a piece of bone in a dilute acid
solution, the inorganic portion of the bone is dissolved out, and the
organic portion, which forms the framework of the bone, is alone left.
On the other hand, by submitting a bone to the action of great heat, the
organic portion of the bone is driven off, and all that remains is a
quantity of ash. The proportion of the organic to the inorganic matter
varies considerably in different bones. The bones of young animals
contain more organic matter than those of old animals. In compact bones,
also, the organic matter is greater than in spongy bones. The
thigh-bone, of all the bones, contains most inorganic matter. In short,
bones which have to bear the greatest strain are richest in inorganic
matter. Of the bones of animals, fish-bones exhibit the greatest variety
of composition, some being almost entirely made up of organic matter,
while others are sim