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capacity connected with a reflux condenser. 350 grms. conc. hydrochloric acid are gradually added in small quantities, the amount being regulated by the reaction, which should proceed steadily. If the contents of the flask begin to boil up violently, the flask is cooled in water until the reaction has somewhat slackened. When nearly the whole of the tin has dissolved, the flask is transferred to the water-bath and heated for about half an hour. The liquid now contains no drops of oil and the smell of nitrobenzene should have disappeared. The contents of the flask, which on cooling solidify to a crystalline mass (a double salt of stannic chloride and aniline hydrochloride) are diluted with water, and strong caustic soda solution added until the stannic oxide, which is first precipitated, nearly redissolves. The aniline, which separates out as a dark-coloured oil, is distilled with steam. For this purpose the apparatus shown in Fig. 12 is employed. The mixture containing the aniline is placed in a flask (B) connected with a condenser, the flask being somewhat inclined to prevent liquid spirting into the neck and being carried over into the receiver. The flask is heated gently on a sand-bath. Steam is passed in from a second flask (A) containing water by a tube which reaches below the level of the liquid to be distilled. A straight vertical tube open at both ends and dipping below the level of the water, prevents the aniline mixture rushing back when the lamp is withdrawn from under the boiling water. Aniline and water collect in the receiver, the former as an almost colourless oil. When no further condensation of oil is observed, the distillation is discontinued and the oil extracted from the distillate by shaking the liquid in a separating funnel two or three times with small quantities (50 c.c.) of ether. The ethereal solution separated as far as possible from water is further
dehydrated by adding a few pieces of solid caustic potash. The clear liquid is decanted into a distilling flask and the ether distilled off on the water-bath, until nothing more passes over.
The residue is distilled over wire gauze. Aniline distils at 181°—182° and has usually a faint amber colour.
2C6H5NO, + 3Sn + 12HCI Nitrobenzene.
2C8H NII, + 3SnCl, + 4H,0
Properties.—Colourless, highly refracting liquid, which quickly darkens in colour; b. p. 182°; sp. gr. 1'0265 at 15°. With bleaching powder solution a drop of the oil gives a blue colour; on heating a few drops of the base with a little alcoholic potash and a drop of chloroform in a test-tube phenylcarbamine is formed, a substance possessing an intolerable smell (Hofmann's reaction for primary amines).
LITERATURE.—Gerhardt (1853), Ann. Ch. Phys. (3) 37, 328 ; G. Williams (1864), Chem. Soc. J. 2, 106.
25 grms. aniline.
Twenty-five grms. aniline and 25 grms. glacial acetic acid are mixed in a retort or flask of about 250 C.c. capacity connected with a straight upright tube or air condenser (Fig. 13) and boiled for about twelve hours. The liquid on cooling solidifies. The contents while warm are therefore at once distilled with a condenser until excess of acetic acid has been expelled and the liquid which passes over begins to solidify (280). The condenser is now removed, the receiver changed and the distillation continued.* Care must be taken, by keeping the neck of the retort warm, that it does not become choked. The acetanilide which solidifies in the receiver has a yellow colour and smells of phenyl carbamine. It may be recrystallised from boiling water and forms colourless
tabular crystals, the purity of which may be ascertained by observing the melting point.
Melting-point determination. For this purpose the following apparatus is used (Fig. 14). A small sample of the finely powdered substance, dried in a desiccator over sulphuric acid, is introduced into a fine capillary tube sealed at one end. The substance is shaken to the bottom of the tube by gently tapping the sealed end. This portion of the tube attached to a thermometer by an india-rubber ring is immersed in conc. sulphuric acid contained in a small beaker, which it half fills. The beaker is gently heated over a small flame until the substance melts. The temperature is then noted.
The lower end of the thermometer bulb and the sealed end of the capillary tube must stand at the same level in the liquid (about 1 to 1 cm. from the bottom of the vessel). The liquid is maintained at a uniform temperature whilst being heated by stirring gently with a glass rod the lower end of which is bent at right angles and then formed into a ring. By