general.

Among those who improved the manufacture of nitro-glycerine was Mowbray,
who, by using pure glycerine and nitric acid free from nitrous acid, made
very great advances in the manufacture. Mowbray was probably the first to
use compressed air for the purpose of keeping the liquids well agitated
during the process of nitration, which he conducted in earthenware pots,
each containing a charge of 17 lbs. of the mixed acids and 2 lbs. of
glycerol.

A few years later (1872), MM. Boutnny and Faucher, of Vonges,[A] proposed
to prepare nitro-glycerine by mixing the sulphuric acid with the
glycerine, thus forming a sulpho-glyceric acid, which was afterwards mixed
with a mixture of nitric and sulphuric acids. They claimed for this method
of procedure that the final temperature is much lower. The two mixtures
are mixed in the proportions--Glycerine, 100; nitric acid, 280; and
sulphuric acid, 600. They state that the rise of temperature upon mixing
is limited from 10° to 15° C.; but this method requires a period of
twenty-four hours to complete the nitration, which, considering the danger
of keeping the nitro-glycerine in contact with the mixed acids for so
long, probably more than compensates for the somewhat doubtful advantage
of being able to perform the nitration at such a low temperature. The
Boutnny process was in operation for some time at Pembrey Burrows in
Wales, but after a serious explosion the process was abandoned.

[Footnote A: _Comptes Rendus_, 75; and Desortiaux, "Traité sur la Poudre,"
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