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 indiarubber will not stand the atmosphere of the nitro-benzole house.  Above and close to each nitrator stands its acid store tank, of iron or stoneware.

The building in which the nitration is carried out should consist of one story, have a light roof, walls of hard brick, and a concrete floor of 9 to 12 inches thick, and covered with pitch, to protect its surface from the action of the acids.  The floor should be inclined to a drain, to save any nitro-benzol spilt.  Fire hydrants should be placed at convenient places, and it should be possible to at once fill the building with steam.  A 2-inch pipe, with a cock outside the building, is advisable.  The building should also be as far as possible isolated.