CHLORAL. (FR., Chloral ; GER., Chloral.) Formula C21:1C180.
Chloral is a peculiar, oily liquid discovered by Liebig, in 1832 ; he obtained it by the action of chlorine upon alcohol. It is colourless, greasy to the touch, and possesses a pungent, ethereal odour. At 18°, it has a specific gravity of 1.502; at 94.4°, it boils, and distils over unaltered. It is soluble in water, alcohol, and ether. When dissolved in a small quantity of water, it forms a semi-solid, crystalline mass of chloral hydrate, which dissolves readily in a larger quantity of water.
The preparation of chloral from alcohol is as follows :—A quantity of absolute alcohol is placed in a glass-stoppered retort, and dry chlorine gas is passed through it. The alcohol should be eold at first, but afterwards heated gently, until, when raised to the boiling-point, the chlorine gas comes through unaltered. The whole is then permitted to cool, when a solid, crystallioe mass of chloral hydrate is formed. This mass is gently heated until it fuses, and is then shaken up with three times its volume of concentrated sulphuric acid. On the application of a gentle heat, a layer of impure chloral rises to the surface ; it is removed, boiled for some time, and distilled with an equal volume of sulphuric acid ; it is finally mixed with quick-lime, and redistilled, in order to romovo traces of hydrochloric acid ; the operation is finished when the surface of the lime becomes dry. The chlorine should he introduced into the retort by means of a bent tube inserted in the tubulure. Another tube, which should be of considerable length, is connected with the stem of the retort, in order to carry away the fumes of hydrochloric acid, and to permit the volatilized alcohol and chloral to recondense and flow back into the vessel.
The hydrate, C,I1C180 • I-120, is the more important compound, since it has lately received several applications iu medicine. The following description of its preparation iu quantity is given by Squire :— Dry chlorine gas is passed for several days, through absolute alcohol, sp. gr. 0.795, until it
becomes a thick, viscid liquid of sp. gr. 1.57. At the beginning of the operation, the alcohol is well cooled, to prevent inflammation and explosion; but towards the end of the operation, the alcohol is heated nearly to the boiling-point. The resulting liquid, which, after a day or two, becomes a solid mass of crude chloral hydrate, is agitated with four times its hulk of concen trated sulphuric acid, and the anhydrous chloral, which floats on the surface, is separated and purified by fractional distillation. The purified anhydrous chloral is placed in a still, mixed with 11 per cent. of water, and distilled over chalk, to remove any hydrochlmic acid that may he present ; the resulting solid distillate is then fused, and poured out into shallow vessels to cast into cakes. To obtain the hydrate in the purest form, it may he dissolved several times in pure bisulphide of carbon, and recrystallized.
Hydrate of chloral is a white, solid, crystalline substance having a pungent, agreeable odour. When dissolved in water, and treated with caustic potnsh, it decomposes, forming chloroform and formiate of potash. When injected into the blood, it combines with the alkali present therein, and the same decomposition occurs, chloroform heing liberated in the system. It is, therefore,. a powerful nareotic, aud is much used as a sedative and soporific. In Dr. Richardson's reports on the physiologieal action of this substance, presented to the British Association in 1869,1870, and 1871, he states that 90 grains will produce a deep sleep, and that 140 grains is a really dangerous dose.
The ordinary dose, taken internally, is from 10 to 60 grains. Its habitual use is much to be con demned, since, when taken constantly, it exerts a most injurious influence upon the system, very aimilar to the effects produced by the habitual consumption of opium. The use of chloral and hydrate of ehloral as auEestlieties was made the subject of a patent hy Dr. Liebreich, of Berlin, in 1869.