§ 195. Chloral Hydrate (C2H3Cl3O2) is made by mixing equivalent quantities of anhydrous chloral[181] and water. The purest chloral is in the form of small, granular, sugar-like crystals. When less pure, the crystals are larger. These melt into a clear fluid at from 48° to 49°, and the melted mass solidifies again at 48·9°. Chloral boils at 97·5°; it is not very soluble in cold chloroform, requiring four times its weight. The only substance with which chloral hydrate may well be confused is chloral alcoholate (C4H7Cl3O2), but chloral alcoholate melts at a lower temperature (45°), and boils at a higher (113·5°); it is easily soluble in cold chloroform, and inflames readily, whereas chloral scarcely burns.
[181] Anhydrous chloral (C2HCl3O) is an oily liquid, of specific gravity 1·502 at 18°; it boils at 97·7°. It is obtained by the prolonged action of chlorine on absolute alcohol.
Chloral hydrate completely volatilises, and can be distilled in a vacuum without change. If, however, boiled in air, it undergoes slow decomposition, the first portions of the distillate being overhydrated, the last underhydrated; the boiling-point, therefore, undergoes a continuous rise. The amount of hydration of a commercial sample is of practical importance; if too much water is present, the chloral deliquesces, especially in warm weather; if too little, it may become acid, and in part insoluble from the formation of meta-chloral (C6H3Cl9O3). Chloral hydrate, by the action of the volatile or fixed alkalies, is decomposed, an alkaline formiate and chloroform resulting thus—
C2HCl3O,H2O + NaHO = NaCHO2 + H2O + CHCl3.
Trichlor-acetic acid is decomposed in a similar manner.
Statistics.—Chloral caused, during the ten years 1883-1892 in England and Wales, 127 deaths—viz., 111 (89 males, 22 females) accidentally, 15 (14 males, 1 female) from suicide, and a case in which chloral was the agent of murder.
§ 196. Detection.—It is, of course, obvious that after splitting up chloral into chloroform, the latter can be detected by distillation and applying the tests given at [p. 152] and seq. Chloral hydrate is soluble in one and a half times its weight of water; the solution should be perfectly neutral to litmus. It is also soluble in ether, in alcohol, and in carbon disulphide. It may be extracted from its solution by shaking out with ether. There should be no cloudiness when a solution is tested with silver nitrate in the cold; if, however, to a boiling solution nitrate of silver and a little ammonia are added, there is a mirror of reduced silver.
§ 197. The assay of chloral hydrate in solutions is best effected by distilling the solution with slaked lime; the distillate is received in water contained in a graduated tube kept at a low temperature. The chloroform sinks to the bottom, and is directly read off; the number of c.c. multiplied by 2·064 equals the weight of the chloral hydrate present.