Prop., &c. A thin, oily, colourless liquid, with a faintly vinous odour, and a hot and aromatic taste; very volatile in the air; miscible in all proportions with alcohol and ether; very slightly soluble in water; neutral to ordinary test-paper, but exhibiting an alkaline reaction to dahlia-petal infusion and paper; dissolves camphor, sulphur, and phosphorus, and coagulates albumen; possesses a high refractive power; and precipitates the oxides of iron, zinc, and alumina, from solutions of their salts, and neutralises the acids, like ammonia. With the acids it forms numerous crystallisable compounds of great beauty, and which are easily formed, and are precisely analogous to the corresponding salts of ammonia. These, on exposure to the air, acquired a rose colour, in many cases gradually passing into brown. Its boiling-point is 359° to 360° Fahr.; sp. gr. 1·028.

Tests.—1. Chromic acid gives a deep greenish or bluish-black precipitate with aniline and its salts:—2. Hypochlorite of lime strikes an extremely beautiful violet colour, which is soon destroyed:—3. The addition of two or three drops of nitric acid to anhydrous aniline produces a fine blue colour, which, on the application of heat, passes into yellow, and a violent reaction ensues, sometimes followed by explosion:—4. With bichloride of platinum it yields a double salt (platino-chloride of aniline)

analogous to the like salt of ammonia. These reactions distinguish it from all other substances.

Commercial aniline is a mixture consisting in great part of aniline, paratoluidine (solid), and orthotoluidine in variable proportions. In addition it contains small amounts of metatoluidine, nitrobenzol, odorine, &c., but for all practical purposes it may be regarded as a mixture of aniline and toluidine. These anilines are obtained from a portion of the light coal-tar naphtha boiling between certain temperatures, by treating it first with nitric acid to convert it into the nitro-compounds, and then reducing these with iron and acetic acid, as already described under Béchamp’s process. It is very plain that as the coal-tar naphtha contains variable proportions of benzol and toluidine, the resulting product must also vary in the quantities of aniline and toluidine it will contain. In order to distinguish between various samples of commercial aniline, Reimann submits them to fractional distillation and compares the results. He places 100 c. c. of the sample to be tested in a retort fitted with a thermometer and heated by means of an oil bath. The liquid as it distils is received in a narrow graduated cylinder, and the amount that passes over between every 5° C. (9° F.) is noted.

In order to obtain standards for comparison he first distilled a sample of light aniline, or kuphaniline, as he terms it, then one of heavy aniline or baraniline; afterwards mixtures of the two in varying proportions. In the accompanying table the results are given.

CentigradeK.100908580756050250
B.010152025405075100
Below 180° 81⁄2721⁄251⁄27...751⁄2...
180°—185° 5450291⁄22251⁄2741⁄221⁄22
185°—190° 3434561⁄2551⁄2551⁄23771⁄241⁄211⁄2
190°—195° ...571⁄281⁄2153342178
195°—200° ............9...193618
200°—205° ............41⁄216101639
205°—210° ..................31⁄2819
210°—215° .....................41⁄27
Residue 31⁄24481⁄231⁄2761⁄2551⁄2

To ascertain the quality of any sample it is only necessary to distil it in the manner already described, and compare the results with those in the above table.

(For further information consult Wagner’s ‘Chemical Technology,’ Calvert’s ‘Dyeing and Calico Printing,’ edited by Stenhouse and Groves; Crooke’s ‘Practical Handbook of Dyeing and Calico Printing,’ Ure’s Dictionary, edited by Hunt.)

Uses, &c. Chiefly in dyeing, for the production of colouring matter of various rich shades of purple and violet, some approaching pink, by the action of chromic acid; and of a splendid crimson, by the action of various oxidising agents. It forms the basis of the celebrated new dyes for silks lately patented by Mr W. H. Perkin, and others, and which are not only more delicate and gorgeous in tint, but also more permanent, than any produced by other substances.

Besides numerous salts, various substitution compounds of aniline have been formed, all of which possess vast scientific interest, and several are likely to prove of importance in the arts. See Dyeing, Indigo, Tar Colours, &c. (also below.)