Nitro-benzene, C_{6}H_{5}(NO_{2}), was discovered in 1834 by Mitscherlich. It is a yellow liquid, with a melting point of +3 deg. C. It has an intense odour of bitter almonds. It solidifies in the cold. In di-nitro-benzene, the two nitro groups may be in the meta, ortho, or para position, the meta position being the most general (see fig., page 4). By recrystallising from alcohol, pure meta-di-nitro-benzene may be obtained in long colourless needles. The ortho compound crystallises in tables, and the para in needles. They are both colourless. When toluene is nitrated, the para and ortho are chiefly formed, and a very little of the meta compound. ~Nitro Compounds of Benzene and Toluene.~--The preparation of the nitro derivatives of the hydrocarbons of the benzene series is very simple. It is only necessary to bring the hydrocarbon into contact with strong nitric acid, when the reaction takes place, and one or more of the hydrogen atoms of the hydrocarbon are replaced by the nitryl group (NO_{2}). Thus by the action of nitric acid on benzene (or benzol), mono-nitro-benzene is formed:-- 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 deg. 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.