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.

The acids are mixed beforehand, and allowed to cool before use. The nitric
acid used has a specific gravity of 1.388, and should be as free as
possible from the lower oxides of nitrogen. The sulphuric acid has a
specific gravity of 1.845, and contains from 95 to 96 per cent. of mono-
hydrate. A good mixture is 100 parts of nitric to 140 parts of sulphuric
acid, and 78 parts of benzene; or 128 parts HNO_{3}, 179 of H_{2}SO_{4},
and 100 of benzene (C_{6}H_{6}). The benzene having been introduced into
the cylinder, the water is turned on and the apparatus cooled, the
agitators are set running, and the acid cock turned on so as to allow it
to flow in a very thin stream into the nitrator.

Should it be necessary to check the machinery even for a moment, the
stream of acid must be stopped and the agitation continued for some time,
as the action proceeds with such vigour that if the benzene being nitrated
comes to rest and acid continues to flow, local heating occurs, and the
mixture may inflame. Accidents from this cause have been not infrequent.
The operation requires between eight to ten hours, agitation and cooling
being kept up all the time. When all the acid is added the water is shut
off, and the temperature allowed to rise a little, to about 100° C. When