Chloral hydrate, CCl3·CH(OH)2, forms oblique, often very short, rhombic prisms. The crystals are perfectly transparent, only slightly odorous, free from powder, and dry to the touch, and do not become white by exposure. The melting-point of pure chloral hydrate is 57°, the boiling-point 96-98° C. When heated with sulphuric acid it is converted into anhydrous chloral and chloralide, C6H2Cl6O3. When mixed with water, chloral hydrate causes a considerable degree of cold; and, as with camphor, small fragments of it placed on the surface of water exhibit gyratory movements. Chloral hydrate does not restore the colour to a solution of fuchsine which has been decolorized by sulphurous acid, and so one must assume that the water present is combined in the molecular condition (V. Meyer, Ber., 1880, 13, p. 2343). Chloral may be estimated by distilling the hydrate with milk of lime and measuring the volume of chloroform produced (C.H. Wood, Pharm. Journ., (3) 1, p. 703), or by hydrolysis with a known volume of standard alkali and back titration with standard acid (V. Meyer, Ber., 1873, 6, p. 600). Chloral hydrate has the property of checking the decomposition of a great number of albuminous substances, such as milk and meat; and a mixture of it with glycerin, according to J. Personne, is suitable for the preservation of anatomical preparations. When heated with concentrated glycerin to a temperature of 110° to 230° C, chloral hydrate yields chloroform, CHCl3, and allyl formate, HCO(OC3H5).
Pharmacology and Therapeutics.—The breaking up of chloral hydrate, in the presence of alkalis, with the production of chloroform and formates, led Liebreich to the conjecture that a similar decomposition might be produced in the blood; and hence his introduction of the drug, in 1869, as an anaesthetic and hypnotic. It is now known, however, that the drug circulates in the blood unchanged, and is excreted in the form of urochloralic acid. The dose is from five to twenty grains or somewhat more, and it is often given in the form of the pharmacopoeial Syrupus Chloral, which contains ten grains of chloral hydrate to the fluid drachm. Chloral hydrate must be well diluted when given by the mouth, as otherwise it may cause considerable gastro-intestinal irritation. In large doses chloral hydrate is a depressant to the circulation and the respiration, and also lowers the temperature. In the above doses the drug is a powerful and safe hypnotic, acting directly on the brain, and producing no preliminary stage of excitement. Very soon—perhaps twenty minutes—after taking such a dose, the patient falls into a sleep which lasts several hours, and is not distinguishable from natural sleep. When he wakes, it is without disagreeable after-symptoms, but with a feeling of natural refreshment. The pupils are always contracted under its influence, except in large doses. There is also rapidly induced a depression of the anterior horns of grey matter in the spinal cord, and as the symptoms of strychnine poisoning are due to violent stimulation of these areas, chloral hydrate is a valuable antidote in such cases. It should not be hypodermically injected. Its disadvantages are that it is powerless when there is pain, resembling in this feature nearly all hypnotics except opium (morphine) and hyoscin. Its action on the gastro-intestinal canal and on the respiratory and circulatory systems renders its use inadvisable when disease of these organs is present. Its action on the spinal cord has been employed with success in cases of tetanus, whooping-cough, urinary incontinence, and strychnine poisoning. In the latter case twenty grains in “normal saline” solution may be directly injected into a subcutaneous vein, but not into the subcutaneous tissues.
Toxicology.—In cases of acute poisoning by chloral hydrate, the symptoms may be summarized as those of profound coma. The treatment is to give a stimulant emetic such as mustard; to keep up the temperature by hot bottles, &c.; to prevent or disturb the patient’s morbid sleep by the injection of hot strong coffee into the rectum; and by shouting, flipping with towels, &c.; to use artificial respiration in extreme cases; and to inject strychnine. Strychnine is much less likely, however, to save life after poisoning by chloral hydrate, than chloral hydrate is to save life in poisoning by strychnine.
Chronic poisoning by chloral is a most pernicious drug-habit. The vice is easily and very rapidly acquired. The victim is usually excited and loquacious. He is easily fatigued and suffers from attacks of easily induced syncope. There are signs of gastro-intestinal irritation, and a tendency to cutaneous eruptions of an erythematous type. The patient may succumb to a dose only slightly larger than usual. The treatment is on general principles, there being no specific remedy. The patient must be persuaded to put himself under restraint, and the drug must be stopped at once and entirely.
CHLORATES, the metallic salts of chloric acid; they are all solids, soluble in water, the least soluble being the potassium salt. They may be prepared by dissolving or suspending a metallic oxide or hydroxide in water and saturating the solution with chlorine; by double decomposition; or by neutralizing a solution of chloric acid by a metallic oxide, hydroxide or carbonate. They are all decomposed on heating, with evolution of oxygen; and in contact with concentrated sulphuric acid with liberation of chlorine peroxide. The most important is potassium chlorate, KClO3, which was obtained in 1786 by C.L. Berthollet by the action of chlorine on caustic potash, and this method was at first used for its manufacture. The modern process consists in the electrolysis of a hot solution of potassium chloride, or, preferably, the formation of sodium chlorate by the electrolytic method and its subsequent decomposition by potassium chloride. (See [Alkali Manufacture].) Potassium chlorate crystallizes in large white tablets, of a bright lustre. It melts without decomposition, and begins to give off oxygen at about 370° C. According to F.L. Teed (Proc. Chem. Soc., 1886, p. 141), the decomposition of potassium chlorate by heat is not at all simple, the quantities of chloride and perchlorate produced depending on the temperature. A very gentle heating gives decomposition approximating to the equation of 22KClO3 = 14KClO4 + 8KCl + 5O2, whilst on a more rapid heating the quantities correspond more nearly to 10KClO3 = 6KClO4 + 4KCl + 3O2. The decomposition is rendered more easy and regular by mixing the salt with powdered manganese dioxide. The salt finds application in the preparation of oxygen, in the manufacture of matches, for pyrotechnic purposes, and in medicine. Sodium chlorate, NaClO3, is prepared by the electrolytic process; by passing chlorine into milk of lime and decomposing the calcium chlorate formed by sodium sulphate; or by the action of chlorine on sodium carbonate at low temperature (not above 35° C). It is much more soluble in water than the potassium salt.
Potassium chlorate is very valuable in medicine. Given in large doses it causes rapid and characteristic poisoning, with alterations in the blood and rapid degeneration of nearly all the internal organs; but in small doses—5 to 15 grains—it partly undergoes reduction in the blood and tissues, the chloride being formed and oxygen being supplied to the body-cells in nascent form. Its special uses are in ulceration of the mouth or tongue (ulcerative stomatitis), tonsillitis and pharyngitis. For these conditions it is administered in the form of a lozenge, but may also be swallowed in solution, as it is excreted by the saliva and so reaches the diseased surface. Its remarkable efficacy in healing ulcers of the mouth—for which it is the specific—has been ascribed to a decomposition effected by the carbonic acid which is given off from these ulcers. This releases chloric acid, which, being an extremely powerful antiseptic, kills the bacteria to which the ulcers are due.
CHLORINE (symbol Cl), atomic weight 35.46 (O = 16), a gaseous chemical element of the halogen group, taking its name from the colour, greenish-yellow (Gr. χλωρός). It was discovered in 1774 by Scheele, who called it dephlogisticated muriatic acid; about 1785, C.L. Berthollet, regarding it as being a compound of hydrochloric acid and oxygen, termed it oxygenized muriatic acid. This view was generally held until about 1810-1811, when Sir H. Davy showed definitely that it was an element, and gave it the name which it now bears.
Chlorine is never found in nature in the uncombined condition, but in combination with the alkali metals it occurs widely distributed in the form of rock-salt (sodium chloride); as sylvine and carnallite, at Stassfürt; and to a smaller extent in various other minerals such as matlockite and horn-mercury. In the form of alkaline chlorides it is found in sea-water and various spring waters, and in the tissues of animals and plants; while, as hydrochloric acid it is found in volcanic gases.