fter the action is over, boil the mixture for a short time,
then pour into about half a litre of water, filter off the crystals thus
produced, press between layers of filter paper, and crystallise from
alcohol. Di-nitro-benzene, or meta-di-nitro-benzene, as it is sometimes
called, enters into the composition of several explosives, such as tonite
No. 3, roburite, securite, bellite.

Nitro-benzene is manufactured upon the large scale as follows:--Along a
bench a row of glass flasks, containing 1 gallon each (1 to 2 lbs.
benzene), are placed, and the acids added in small portions at a time, the
workmen commencing with the first, and adding a small quantity to each in
turn, until the nitration was complete. This process was a dangerous one,
and is now obsolete. The first nitro-benzene made commercially in England,
by Messrs Simpson, Maule, and Nicholson, of Kennington, in 1856, was by
this process. Now, however, vertical iron cylinders, made of cast-iron,
are used for the nitrating operation. They are about 4 feet in diameter
and 4 feet deep, and a series are generally arranged in a row, at a
convenient height from the ground, beneath a line of shafting. Each
cylinder is covered with a cast-iron lid having a raised rim all round. A
central orifice gives passage to a vertical shaft, and two or more other
conveniently arranged openings allow the benzene and the mixed acids to
flow in. Each of these openings is surrounded with a deep rim, so that the
whole top of the cylinder can be flooded with water some inches in depth,
without any of it running into the interior of the nitrator. The lid
overhangs the cylinder somewhat, and in the outer rim a number of shot-
holes or tubes allow the water to flow down all over the outside of the
cylinder into a shallow cast-iron dish, in which it stands. By means of a
good supply of cold water, the top, sides, and bottom of the whole
apparatus is thus cooled and continually flooded. The agitator consists of
cast-iron arms keyed to a vertical shaft, with fixed arms or dash-plates
secured to the sides of the cylinder. The shaft has a mitre wheel keyed on
the top, which works into a corresponding wheel on the horizontal shafting
running along the top of the converters. This latter is secured to a
clutch; and there is a feather on the shaft, so that any one of the
converters can if necessary be put either in or out of gear. This
arrangement is necessary, as riggers or belts of leather, cotton, or