Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/691

Rh CHLORAL 677 A mixture of starch or sugar with manganese peroxide and hydrochloric acid may be employed instead of alcohol and chlorine for the manufacture of chloral (Stadeler, Aim. Ch. Pharm., Ixi. 101-121). An isomer of chloral, paracldoralide, is made by passing excess of dry chlorine into absolute methylic alcohol ; it is a colourless liquid, insoluble in water, and boils at 182 C. (Cloez, Ann. Ch. Pharm., iii. 180). Chloral hydrate, C,C1 3 OH.II 2 0, or CC1 3 .CH(OH) 2, the compound formed by the union of water with chloral, occurs in the form of oblique, often very short, rhombic prisms ; an acicular form of crystals is considered by Paul to be characteristic only of the alcoholate. The purest samples of chloral hydrate present the appearance of ordinary alum broken into fragments, are perfectly transparent, only slightly odorous, free from powder, and dry to the touch, and do not become white by exposure. Jacobsen gives the melting point of pure chloral hydrate as 50 to 51, the boiling point as 99 C. It can be distilled unchanged at 120C. ; but when heated with sulphuric acid it is converted into anhydrous chloral and chloralide, C 5 H 2 C1 G O 3. 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 move ments. An aqueous solution should bo neutral or nearly so, and should give but a faint milkiness when boiled with silver nitrate. A drop or two of ammonia added to solu tions assists in their preservation. Chloral hydrate may be detected in the presence of other substances by adding an alkali and heating, when chloroform is evolved, which may be collected in a receiver ; this process can be employed for the estimation of the commercial hydrate. When ammonium sulphide is added to a solution of pure chloral hydrate, the liquid turns red, and then becomes rapidly brown and thick ; the presence of oily impurities in a solution is shown by the brown colour it acquires when shaken up with concentrated sulphuric acid. 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 glycerine, according to Personne, is suitable for the preservation of anatomical preparations. When heated with concentrated glycerine to a temperature of 110-230C., chloral hydrate yields chloroform, CHC1 3, and formate of allyl, HCO(OC 3 H 5 ) ; and by the action of nitric acid and strong sunlight, at 195 C. it is transformed into trichloracetic acid, CC1 3 .COOH. The effect of chloral hydrate upon fresh blood, like that of formic acid, is to render it darker. The breaking up of chloral hydrate, in the presence of alkalies, with the production of chloroform and formates, led Liebreichto 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 (Compt. rend., 1869, Ixix., 486). It has been supposed that its physiological action may be due to formic acid as well as to chloroform set free in the blood, the effects of the formic acid being attributed to the production from it of carbon dioxide. Personne, however, has administered sodium formate to dogs, without perceiving in them the slightest anaesthetic phenomena, or the abnormal formation of carbon dioxide (Compt. rend., 1874, Ixxviii. 12P). He considers that chloroform is set free in the blood, but is not eliminated as such, being converted into sodium chloride and formate (ibid. 1869, Ixix., 983); the prolonged action of chloral on the animal economy he explains on the supposition that, chloroform being produced at the expense of the alkali of the albumen of the blood, the latter, which may be regarded as an amide, forms with the trichlorinated aldehyde chloral a compound which, by the gradual action cf he blood, affords a continuous supply of chloroform. Tanret, on the other hand, suggests that as chloral hydrate, when made alkaline with caustic potash, yields in the presence of the oxidizing agent potassium permanganate the formate, chloride, and carbonate of potassium, together with carbon monoxide, the alkalinity of the serum of the blood may determine a similar decomposition of chloral hydrate, the physiological effects of which may therefore be ascribed to poisoning or deoxidation of arterial blood by carbon monoxide (Compt. rend., Ixxix. 662 ; Journ. Pharm. Chim. (4), xx. 355-357). The first effect of a dose of chloral hydrate is to produce a state of congestion of the brain, as evidenced by the con dition of the retinal vessels ; after 5 or 10 minutes, con traction of the vessels is observed, the retina becomes of a pale pink colour, and drowsiness ensues ; when this wears off, the retinal and cerebral vessels resume their accustomed size (Dr W. A. Hammond). In cases of death from chloral, the cerebral vessels have been found much congested. The effects of chloral hydrate vary with different individuals; but, as a rule, a dose of 20 grains acts in a healthy subject as a mild sedative of the sensory nervous system, and produces, about half or three quarters of an hour after it has been taken, a light, refreshing, and normal sleep, without causing headache or disturbance of the respiration and pulse. Taken in large quantities chloral hydrate is a powerful soporific ; it perceptibly lowers the temperature of the body, and diminishes the frequency and force of the heart s action, probably from paralysis of its intrinsic motor- ganglia ; whilst the rate of respiration is lessened, apparently through affection of the medulla oblongata. Ex cessive doses produce complete insensibility, and diminish, and at last abolish reflex excitability ; pallor, coldness of the extremities, lividity, and muscular relaxation ensue ; and death may result from cardiac syncope. M Ore&quot; is the originator of a plan for performing opera tions during anaesthesia produced by the intra-venous injection of chloral hydrate. He shows (Compt. rend., 1874, Ixxviii. 515, 651) that it may be harmlessly injected, and that when thus brought into immediate contact with the blood, it effects complete anaesthesia of long duration, and is a rapid and effectual remedy for tetanus. Chloral hydrate sometimes fails to afford relief from suffering, and when it does not induce sleep, may occasion excitement and delirium. In some cases a dose has produced an eruption of urticaria. It must be administered with caution to children, and to patients having disease of the heart and of the digestive tract, certain affections of the bronchi, or hysteria. It appears that chloral cannot be decomposed and thrown off by a healthy body at a greater rate than from 5 to 7 grains an hour (Richardson, Lancet, 1871, 1, 209); and as the limit of the dose that can be safely taken is not affected by the customary use of the drug, as in the case of opium, but rather the reverse, its incautious employment in large quantities, and the practise of habitually resorting to it to gain relief from sleeplessness, from neuralgia, and from the effects of alcoholic excess, have in not a few instances led to fatal results. In consequence of this risk medical practitioners now use it less extensively. The continued use of chloral hydrate, too, is apt to cause a hyperaemic condition of the skin, diffuse inflammatory erythema of the face and chest, conjunctivitis, and interference with re spiration ; and may bring on deep melancholy, weakness of will, and inability to sleep without the drug. Chloral hydrate is of special value as a soporific where opium is inadmissible, as in the case of children, in uraemia, and in some fevers, It is used in delirium tremens, rabies, severe chorea, acute mania, and phthisis, as well as in dyspnoea, pertussis, cholera, sea-sickness, cancer, chronic rheumatism, and gastralgia, and in parturition and eclampsia;