Properties.-Large green foliated crystals; m. p. 85°; somewhat volatile in steam. If a solution of the hydrochloride be saturated with HS and ferric chloride added to the liquid, a deep blue coloration is produced from the formation of methylene blue (Ber. II, 1705).

PREPARATION XI.

PARA-NITROSOPHENOL, C ̧H ̧NO2=CH(1)

(Quinonoxime.)

2 4(4)N.OH.

LITERATURE.-Baeyer, Caro (1874), Ber. 7, 809 and 963; Ter Meer (1875), Ber. 8, 622; Goldschmidt (1884), Ber. 17, 214.

5 grms. nitrosodimethylaniline hydrochloride.

Twenty-five grms. caustic soda solution (sp. gr. 125) and 225 grms. water are heated to boiling in a round-bottomed flask connected with a condenser and receiver containing dilute hydrochloric acid. Five grms. nitrosodimethylaniline are gradually added to the soda solution by removing the cork for a moment. The free base, which separates out in oily drops, is allowed to dissolve before each fresh addition. The

boiling is continued until the dark green colour of the liquid changes to reddish yellow. The greater part of the dimethylamine, formed simultaneously with the nitrosophenol, passes over with the aqueous vapour and is absorbed in the receiver.1 The liquid in the flask is thoroughly cooled, acidified with dilute sulphuric acid and extracted with ether. On distilling off the greater part of ether from the dark green solution, the nitrosophenol remains in brown foliated. crystals, which are separated from the mother-liquor and dried.

Properties. Brown foliated crystals; soluble in hot water, alcohol, and ether; decomposes at 120°-130° with slight explosion leaving a residue of carbon. Dissolved in excess of phenol it gives on the addi tion of a few drops of conc. sulphuric acid a cherry-red solution, which changes to blue on the addition of water and caustic alkali (Liebermann's "nitroso" reaction).

1 On evaporating down the hydrochloric acid solution on the water-bath colourless crystals of dimethylamine hydrochloride may be obtained.

PREPARATION XII.

POTASSIUM BENZENE SULPHONATE, CH,.SOK.

LITERATURE.-Mitscherlich (1834), Pogg. Ann. 31, 283 and 364; Michael, Adair (1877), Ber. 10, 585.

One hundred grms. pure commercial benzene and 200 grms. conc. sulphuric acid are mixed together in a round-bottomed flask of about litre capacity, provided with a reflux condenser, and the mixture. kept at a gentle boil on the sand-bath for about twenty-four hours. The contents of the flask divide into two layers. The lower layer of acid assumes a dense black colour, and gradually increases in volume as the boiling continues, the upper layer of benzene diminishing in the same proportion until about fourfifths of the benzene has dissolved, when more prolonged heating produces no further change. After cooling, a portion of the unattacked benzene may be separated by means of a tap-funnel. The darkcoloured acid liquid is poured into a large volume (about 1 litre) of water, and any residual benzene is distilled off with steam. The liquid is then neutralised whilst hot with powdered chalk mixed into a paste with water or with milk of lime. The mass is filtered hot

through cloth from the precipitate of calcium sulphate, washed with hot water, and the faintly brown coloured filtrate carefully concentrated over the flame until a sample, withdrawn on the end of a glass rod, on cooling solidifies. From the solution the calcium salt of benzene sulphonic acid separates out on cooling, and forms an almost solid mass of small, white crystals, which, after being drained from the mother-liquor, are almost pure. In order to convert the calcium salt into the corresponding potassium salt, the former is dissolved in water, and, whilst hot, a concentrated solution of potassium carbonate carefully added, until the calcium is exactly precipitated as calcium carbonate. The aqueous solution of the potassium salt is filtered from the calcium carbonate through cloth and evaporated down first over the flame and finally on the water-bath until a sample crystallises on cooling. The potassium salt crystallises in the form of colourless crystalline plates, which after filtration and thoroughly drying on unglazed earthenware (a porous plate or tile) are sufficiently pure for further treatment.

Properties.-Colourless, pearly plates which slowly.

effloresce in the air, and which melt above 300° with slight decomposition; very soluble in water, with difficulty in alcohol.

PREPARATION XIII.

PHENOL, CHO = C&H,(OH).
(Carbolic acid, Oxybenzene.)

LITERATURE.-Runge (1834), Berz. Jahresb. 15, 417; Laurent (1842), Ann. Ch. Phys. (3) 3, 195; Gerhardt (1843), Ann. Ch. Pharm. 45, 25; Kekulé, Wurtz, Dusart (1867), Zeitsch. f. Ch. N. S. 3, 299, 300, 301; Degener (1878), Journ. prakt. Ch. (2), 17, 394.

20 grms. potassium benzene sulphonate
caustic potash.

35

Thirty-five grms. caustic potash, dissolved in the smallest quantity of water, are heated in a silver. basin, preferably in the oil-bath (Fig. 15), and 20 grms. dry powdered potassium benzene sulphonate added, the mixture being well stirred.1 The temperature of the oil-bath is maintained at 290°-295° for one hour. In progress of fusion

1 Fusions with strong potash solution under pressure in many cases give better yields. For laboratory purposes a strong steel tube, capable of resisting a high pressure, and closed by a screw plug, is used and heated in a paraffin or oil bath. The fusion requires more time and is made at a lower temperature.