e,"
684-686.]

Nitro-glycerine is now generally made by adding the glycerine to a mixture
of sulphuric and nitric acids. The sulphuric acid, however, takes no part
in the reaction, but is absolutely necessary to combine with the water
that is formed by the decomposition, and thus to keep up the strength of
the nitric acid, otherwise lower nitrates of glycerine would be formed
that are soluble in water, and which would be lost in the subsequent
process of washing to which the nitro-compound is subjected, in order to
remove the excess of acids, the retention of which in the nitro-glycerol
is very dangerous. Nitro-glycerol, which was formerly considered to be a
nitro-substitution compound of glycerol, was thought to be formed thus--

C_{3}H_{8}O_{3} + 3HNO_{3} = C{3}H_{5}(NO_{2})_{3}O_{3} + 3H_{2}O;

but more recent researches rather point to its being regarded as a nitric
ether of glycerol, or glycerine, and to its being formed thus--

C_{3}H_{8}O_{3} + 3 HNO_{3} = C{3}H_{5}(NO_{3})_{3} + 3H_{2}O.
92 227

|OH
The formula of glycerine is C_{3}H_{8}O_{8}, or C_{3}H_{5}|OH
|OH

|ONO_{2}
and that of the mono-nitrate of glycerine, C_{3}H_{5}|OH
|OH

|ONO_{2}
and of the tri-nitrate or (nitro-glycerine), C_{3}H_{5}|ONO_{2}
|ONO_{2}

that is, the three hydrogens of the semi-molecules of hydroxyl in the
glycerine have been replaced by the NO_{2} group.

In the manufacture upon the large scale, a mixture of three parts by
weight of nitric acid and five parts of sulphuric acid are used. From the
above equation it will be seen that every 1 lb. of glycerol should give
2.47 lbs. of nitro-glycerol ((227+1)/92 = 2.47), but in practice the yield
is only about 2 lbs. to 2.22, the loss being accounted for by the
unavoidable formation of some of the lower nitrate, which dissolves in
water, and is thus washed away, and partly perhaps to the presence of a
little water (or other non-nitrable matter) in the glycerine, but chiefly
to the former, which is due to the acids having become too weak.

CHAPTER II.

_MANUFACTURE OF NITRO-GLYCERINE._

Properties of Nitro-Glycerin