Nitro-Explosives: A Practical Treatise

by P. Gerald Sanford

C_{6}H_{6} + HNO_{3} = C_{6}H_{5}.NO_{2} +H_{2}O.
Mono-nitro-benzene.

By the action of another molecule of nitric acid, the di-nitro-benzene is formed:—

C_{6}H_{5}.NO_{2} + HNO_{3} = C_{6}H_{4}(NO_{2}){2} + H{2}O.
Di-nitro-benzene.

These nitro bodies are not acids, nor are they ethereal salts of nitrous acid, as nitro-glycerine is of glycerine. They are regarded as formed from nitric acid by the replacement of hydroxyl by benzene radicals.

~Mono-nitro Benzene~ is made by treating benzene with concentrated nitric acid, or a mixture of nitric and sulphuric acids. The latter, as in the case of the nitration of glycerine, takes no part in the reaction, but only prevents the dilution of the nitric acid by the water formed in the reaction. Small quantities may be made thus:—Take 150 c.c. of H_{2}SO_{4} and 75 c.c. HNO_{3}, or 1 part nitric to 2 parts sulphuric acid, and put in a beaker standing in cold water; then add 15 to 20 c.c. of benzene, drop by drop, waiting between each addition for the completion of the reaction, and shake well during the operation. When finished, pour contents of beaker into about a litre of cold water; the nitro-benzol will sink to the bottom. Decant the water, and wash the nitro-benzol two or three times in a separating funnel with water. Finally, dry the product by adding a little granulated calcium chloride, and allowing to stand for some little time, it may then be distilled. Nitro-benzene is a heavy oily liquid which boils at 205° C., has a specific gravity of 1.2, and an odour like that of oil of bitter almonds. In the arts it is chiefly used in the preparation of aniline.

~Di-nitro Benzene~ is a product of the further action of nitric acid on benzene or nitro-benzene. It crystallises in long fine needles or thin rhombic plates, and melts at 89.9° C. It can be made thus:—The acid mixture used consists of equal parts of nitric and sulphuric acids, say 50 c.c. of each, and without cooling add very slowly 10 c.c. of benzene from a pipette. After 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 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.

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 it ceases to rise the agitators are thrown out of gear, and the mixture allowed some hours to cool and settle. The acid is then drawn off, and the nitro-benzene is well washed with water, and sometimes distilled with wet steam, to recover a little unconverted benzene and a trace of paraffin (about .5 per cent. together). At many English works, 100 to 200 gallons, or 800 to 1,760 lbs., are nitrated at a time, and toluene is often used instead of benzene, especially if the nitro-benzene is for use as essence of myrbane. The waste acids, specific gravity 1.6 to 1.7, contain a little nitro-benzene in solution and some oxalic acid. They are concentrated in cast-iron pots and used over again.