operation of "after-separation," are carried out in one vessel. The usual
nitrating vessel is provided with an acid inlet pipe at the bottom, and a
glass separation cylinder with a lateral exit or overflow pipe at the top.
This cylinder is covered by a glass hood or bell jar during nitration to
direct the escaping air and fumes into a fume pipe where the flow of the
latter may be assisted by an air injector. The lateral pipe in the
separation cylinder is in connection with a funnel leading to the prewash
tank. The drawing (Fig. 7) shows a vertical section of the apparatus; _a_
is the nitrating vessel of usual construction, having at the bottom an
acid inlet pipe with three branches, one leading to the de-nitrating
plant, _c_ leading to the drowning tank, and _d_, which extends upwards
and has two branches, _e_ leading to the nitrating acids tank, and _f_ to
the waste acid tank. On the sloped bottom of the nitrating vessel _a_ lies
a coil _g_ of perforated pipe for blowing air, and there are in the vessel
several coils _h_, three shown in the drawing, for circulation of cooling
water. At the top of the vessel there is a glass cylinder _i_, having a
lateral outlet _j_ directed into the funnel mouth of a pipe _k_ leading to
the prewash tank. Over the cylinder _i_ is a glass globe _l_, into which
opens a pipe _m_ for leading off fumes which may be promoted by a
compressed air jet from a pipe _r_ operating as an injector. Into an
opening of the glass dome _l_ is inserted a vessel _n_, which is connected
by a flexible pipe _p_ to the glycerine tank, and from the bottom of _n_,
which is perforated and covered with a disc perforated with holes
registering with those through the bottom, this disc being connected by a
stem with a knob _q_ by which it can be turned so as to throttle or cut
off passage of glycerine through the bottom. _s_ is a thermometer for
indicating the temperature of the contents of the vessel.

[Footnote A: Eng. Pat. 15,983, August 1901.]