CHLOROFORM, Trichloromethane, Terchloride of Formyl, or Dichlorinated Μ ethylic Chloride, CHC1 3 , is a substitution-product of marsh-gas, CH 4 , from which it can be formed by the action of chlorine. It is a clear, colourless, volatile liquid, which refracts light strongly, with specific gravity of 1 ’ 525 at 0° C., and vapour density 1-491. It boils at 60Ι6° C. (Régnault), and is not frozen at a temperature of — 16° C. It has an agreeable ethereal odour, a slightly acrid and intensely sweet taste, is miscible in all proportions with alcohol, but is only slightly soluble in water. Though not ordinarily inflammable, it burns with a green flame when thrown upon hot coals, or if a light be applied to a mixture of it with not less than about 30 per cent, of alcohol. Chloroform may be employed as a solvent for resin, camphor, gutta-percha, iodine, bromine, and the alkaloids. It can be prepared in a great variety of ways :—(1) By the action of alkalies on chloral (see Chloral); (2) by boiling trichloracetic acid, CC1 3 .CO(OH), with aqueous solutions of the alkalies; (3) by the replacement of an atom of chlorine in carbon tetrachloride, CC1 4 , by nascent hydrogen; (4) on the large scale for commercial purposes by the action of bleaching powder on ethylic alcohol and other carbon compounds. About 8 S> of slaked lime, and 80 S> of the strongest chloride of lime, and 22 gallons of water at a temperature of 80°-90° C. are introduced into a leaden vessel or wooden cask, and thoroughly mixed. Two lb of alcohol are then poured in; and if the heat evolved in the ensuing reaction is not sufficient to distil over the chloroform, a current of steam is passed into the vessel. The crude distillate is purified by washing with water and agitation with sulphuric acid, and by ...redistillation, finally, with a small quantity of slaked lime and calcium chloride, by means of a water-bath. The chief impurities to which chloroform is liable are ether, alcohol, aldehyde, hydrochloric, hypochlorous, and sulphuric acids, chloral, and heavy volatile oils. Pure chloroform does not become opalescent in contact with water, and is not coloured yellow or brown by sulphuric acid, or green by chromic acid; with the former, it gradually evolves hydrochloric acid. When exposed to air and light, chloroform becomes decomposed, with the formation of chlorine, hydrochloric acid, carbon tetrachloride, and other products. The presence of chloroform can be detected by adding to the liquid to be tested for it a monamine, such as aniline, N(C 0 H 5 )H 2 , and an alcoholic solution of caustic potash, when the characteristic odour of the carbamines is given off at once, or on the application of heat.
The history of chloroform affords but one amongst many instances of the importance of chemical research even when no immediate practical advantages are apparently to be derived from its prosecution. Chloroform was discovered in 1831 by Guthrie in America, and by Soubeiran in France, and by the latter was described as ether bichlorique. Liebig, who made the independent discovery of it in the following year, regarded it as a trichloride of carbon; but in 1834 its true constitution was established by Dumas. In March 1847 Flourens submitted to the Academy of Sciences at Paris a paper containing observations on the anaesthetic powers of chloroform upon animals. In the summer of that year “chloric ether,” the active principle of which is chloroform, was used at St Bartholomew’s Hospital by Mr Lawrence instead of sulphuric ether for the production of anaesthesia; and in the succeeding autumn Dr J. Y. Simpson of Edinburgh introduced the employment of pure chloroform as an anaesthetic into surgical practice. By its effect upon the nervous system chloroform causes a suspension of voluntary motion and of sensation, whilst respiration and the action of the sympathetic ganglia of the heart are still continued. It is more active, occasions less bronchial irritation, and is easier of application than ether, the use of which in British practice it has to a very great extent superseded; it possesses also the advantage that its vapour is uninflammable. The occurrence, however, from time to time, of deaths in consequence of the use of chloroform, has led many practitioners to recommend the employment of ether in its stead; but in the majority of instances fatal results may be attributed to some fault in administration; and in some cases death has been thought to be attributable to the giving of a less than customary quantity of chloroform, which, paralyzing the cerebral hemispheres, but not the ganglia of the base of the brain and the medulla, has permitted reflex action of the vagus upon the heart through irritation of a sensory nerve. In operations after which disturbance of the abdomen must be avoided, ether is far preferable to chloroform, on account of the sickness usual for some time after the taking of the latter.
Snow, Anaesthetics ; Holmes, System of Surgery, 2d ed., vol. V. 480 (1871).
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