cture of nitro-glycerine or gun-cotton.

Two points in the manufacture of nitro-glycerine are of the greatest
importance, viz., the purity of the glycerine used, and the strength and
purity of the acids used in the nitration. With regard to the first of
these, great care should be taken, and a complete analysis and thorough
examination, including a preliminary experimental nitration, should always
be instituted. As regards the second, the sulphuric acid should not only
be strong (96 per cent.), but as free from impurities as possible. With
the nitric acid, which is generally made at the explosive works where it
is used, care must be taken that it is as strong as possible (97 per cent.
and upwards). This can easily be obtained if the plant designed by Mr
Oscar Guttmann[A] is used. Having worked Mr Guttmann's plant for some
time, I can testify as to its value and efficiency.

[Footnote A: "The Manufacture of Nitric Acid," _Jour. Soc. Chem. Ind._,
March 1893.]

Another form of nitric acid plant, which promises to be of considerable
service to the manufacturer of nitric acid for the purpose of nitrating,
is the invention of the late Mr Manning Prentice, of Stowmarket. Through
the kindness of Mr Prentice, I visited his works to see the plant in
operation. It consists of a still, divided into compartments or chambers
in such a manner that the fluid may pass continuously from one to the
other. The nitric acid being continuously separated by distillation, the
contents of each division vary--the first containing the full proportion
of nitric acid, and each succeeding one less of the nitric acid, until
from the overflow of the last one the bisulphate of soda flows away
without any nitric acid. The nitrate of soda is placed in weighed
quantities in the hopper, whence it passes to the feeder. The feeder is a
miniature horizontal pug-mill, which receives the streams of sulphuric
acid and of nitrate, and after thoroughly mixing them, delivers them into
the still, where, under the influence of heat, they rapidly become a
homogeneous liquid, from which nitric acid continuously distils.

Mr Prentice says: "I may point out that while the ordinary process of
making nitric acid is one of fractional distillation by time, mine is
fractional distillation by space." "Instead of the operation being always
at the same point of space, but differing by the successive points of
time, I arrange for the differences to take place at different points