Chloral (synonymes, trichlormethyl, hydrocarbon oxide, trichloraldehyde, trichlorace-tyl, oxide hydrate), a chemical compound first obtained by Liebig in 1831 by the action of chlorine upon absolute alcohol. The name is composed of the first syllables of the words chlorine and alcohol. Although Liebig first prepared chloral, we are chiefly indebted to Dumas for a knowledge of its properties and constitution. It is obtained by passing dry chlorine gas though absolute alcohol as long as it is absorbed, during many hours, keeping the vessel cool in the early stages of the operation; later the temperature must be gradually raised until the liquid boils. The reaction is represented by the formula C2H6O + 8 Cl=C2HC130 + 5HCl. If dilute alcohol be employed instead of the absolute, no chloral is formed, but in its stead aldehyde, acetic acid, and hydrochloric acid; hence the necessity of using absolute alcohol. It is also difficult to prevent the formation of other compounds, especially chloride of carbon, which serve to contaminate the chloral and render its administration dangerous.

Chloral is also produced by the direct action of chlorine on aldehyde, also on starch or sugar. - Chloral is a limpid, colorless, oily liquid, with a fatty taste and a strong caustic smell, producing lachry-mation. Its specific gravity is 1.502, and it boils at 95° C, and can be distilled unchanged. It dissolves sulphur, phosphorous, bromine, and iodine, and combines directly with water to form a hydrate. A little chloral put into a moist fiask deposits star-shaped crystals of the hydrate on the sides. It changes after a time into a porcelain-like mass called metachloral, which is insoluble, though isomeric with, the liquid form. It can be reconverted into chloral by distillation. The white metachloral is insoluble in alcohol and ether, as well as in water, but by contact with water it is gradually converted into the crystallized hydrate of chloral. Fuming nitric acid converts chloral into trichloracetic acid. An alcoholic solution of potash converts chloral into formiate of potash and chloroform. Chloral is closely allied to aldehyde; it reduces silver from the ammonia nitrate solution, and forms crystalline compounds with ammonia and the acid sulphites of the alkalies. Nascent hydrogen converts it into aldehyde.

If chloral be mixed with one equivalent of alcohol, white transparent hydroscopic crystals of chloral-alcoholate are formed. This compound has different properties from the hydrate of chloral, and ought not to be mistaken for it. Chloral combined with one equivalent of water forms a crystalline mass, now popularly known under the name of chloral hydrate. According to Dr. Squibb, when the water of hydration is in excess, or when solid compounds of hydrate of chloral and water are put up, the substance is deliquescent, or even melts in warm weather, and a very slight excess of water manifests itself very soon by some degree of deliquescence. Whether in a cake or crystal, it is now very generally put up slightly deficient in water of hydration; that is, the chloral is not fully saturated to a hydrate, which gives the best product for preservation. Accuratelv, hvdrated chloral crystallizes at about 48° to 49° C.(118.4° to 120.2° F.). A little ammonia may be added to prevent acid reaction, and all acid hydrate of chloral should be rejected. The hydrate of chloral is readily dissolved by water, alcohol, ether, oil of turpentine, benzole, bisulphide of carbon, and the fixed oils.

When equal parts of camphor in small pieces and hydrate of chloral in crystals are allowed to stand in a flask, they form a clear solution. The analysis of chloral hydrate is accomplished by measuring in a graduated tube the amount of chloroform liberated by a given quantity of potash. - The enormous production of chloral hydrate has led to an investigation of its possible application in the arts and of uses for the incidental products accompanying its preparation. The precious metals are easily produced by chloral hydrate and caustic alkalies. A large quantity of hydrochloric ether appears as a by-product in the manufacture of chloral, and is applied to the preparation of ethyl ammonias. A mixture of hydrate of chloral with three times its weight of fuming nitric acid is allowed to stand in the direct sunlight for three or four days until red fumes no longer appear; it is then distilled at a temperature of 194° C, and the product is found to be pure trichloracetic acid. - Chloral hydrate was brought forward as an anaesthetic and hypnotic by Dr. Otto Liebreich in 1809. In the presence of alkalies chloral hydrate is decomposed into chloroform and formic acid; the latter unites with the alkali.

The decomposition is supposed by Liebreich to take place in the blood, and the chloroform which is thus set free acts in the usual manner. This is almost the only example of an a priori discovery of a useful drug, and it is therefore to be regretted that the chemical evidence of such a transformation as that just indicated actually taking place in the blood is not more complete. Chloral hydrate, or as it is very frequently called chloral, has proved to be a valuable addition to the materia mediea, although it cannot replace chloroform or ether as a surgical anaesthetic. It produces when acting favorably a quiet and natural sleep, although in rare cases no effect is observed from ordinary doses, and in some instances delirium arises from it. The average dose is from 15 to 30 grains. More than 30 grains at once has sometimes produced alarming symptoms. Death has resulted from still larger doses. It is a drug which should always be administered with caution, even in small doses. It is used to procure sleep in wakefulness from various causes and in many nervous diseases, as insanity, delirium tremens, neuralgia, tetanus, and strychnia poisoning. It is said that the use of chloral as a narcotic without medical advice is becoming a not infrequent habit.

Properly administered, it will produce sleep, diminish sensibility and irritation, relax spasmodic action, and contract the arterioles of the system. Improperly used, it will retard the pulse, alter the blood globules, lower the temperature, and produce anaesthesia, muscular relaxation, and death. It should always be given largely diluted with water. The solutions of chloral hydrate in gum water, sirup, etc, undergo spontaneous decomposition, and become dangerous. The tinctures and anodynes kept on sale should be avoided.