f nitric acid,
and 10 cwt. of sulphuric acid, and 247 lbs. of glycerine.

Upon reference to the equation showing the formation of nitro-glycerine,
it will be seen that for every 1 lb. of glycerine 2.47 lbs. of nitro-
glycerine should be furnished,[A] but in practice the yield is only a
little over 2 lbs., the loss being accounted for by the unavoidable
formation of some of the lower nitrate of glycerine (the mono-nitrate),
which afterward dissolves in the washing waters. The lead tank (Fig. 5) is
generally cased in woodwork, with a platform in front for the man in
charge of the nitrating to stand upon, and whence to work the various
taps. The top of the tank is closed in with a dome of lead, in which is a
small glass window, through which the progress of the nitrating operation
can be watched. From the top of this dome is a tube of lead which is
carried up through the roof of the building. It serves as a chimney to
carry off the acid fumes which are given off during the nitration. The
interior of this tank contains at least three concentric spirals of at
least 1-inch lead pipe, through which water can be made to flow during the
_whole_ operation of nitrating. Another lead pipe is carried through the
dome of the tank, as far as the bottom, where it is bent round in the form
of a circle. Through this pipe, which is pierced with small holes, about 1
inch apart, compressed air is forced at a pressure of about 60 lbs. in
order to keep the liquids in a state of constant agitation during the
whole period of nitration. There must also be a rather wide pipe, of say 2
inches internal diameter, carried through the dome of the tank, which will
serve to carry the mixed acid to be used in the operation into the tank.
There is still another pipe to go through the dome, viz., one to carry the
glycerine into the tank. This need not be a large bore pipe, as the
glycerine is generally added to the mixed acids in a thin stream (an
injector is often used).

[Footnote A: Thus if 92 lbs. glycerine give 227 lbs. nitro-glycerine,
(277 x 1)/92 = 2.47 lbs.]

[Illustration: FIG. 5.--TOP OF NITRATOR. _A_, Fume Pipe; _B_, Water Pipes
for Cooling; _C_, Acid Mixture Pipe; _E_, Compressed Air; _G_, Glycerine
Pipe and Funnel; _T_, Thermometer; _W_, Window.]

Before the apparatus is ready for use, it requires to have two
thermometers fixed, one long one to reach to the bottom of the tank, and
one short one just long enough to dip under the surface of