CHLOROFORM, a valuable anaesthetic first prepared by J. v. Liebig and E. Soubeiran (1831). It is a colourless liquid (trichloromethane, possessing an agreeable smell and a pleasant taste. It may be prepared by the action of bleaching powder on many carbon compounds, but preferably ethyl alcohol and acetone, by heating trichloroacetic acid with ammonia or by alkaline hydrolysis of chloral (q.v.). In the preparation of chloro form by the action of bleaching powder on ethyl alcohol it is probable that the alcohol is first oxidized to acetaldehyde, which is subsequently chlorinated and then decomposed. Chloroform solidifies in the cold and then melts at —62° C. ; it boils at 61.2° C., and has a specific gravity 1.52637 (o° C./4° C.) (T. E. Thorpe). It is an exceedingly good solvent, especially for fats, alkaloids and iodine. It is not inflammable. Chromic acid or exposure to light converts it into phosgene (carbonyl chloride, It reacts with sodium ethylate to form orthoformic ester, CH 3. When digested with phenols and caustic soda it forms hydroxyal dehydes (K. Reimer) ; and when heated with alcoholic potash it is converted into potassium formate.
Chloroform may be readily detected by the production of an isonitrile when it is heated with alcoholic potash and a primary amine ; thus with aniline the nauseating odour of phenyl isocyanide is produced.
For the use of chloroform as an anaesthetic, see ANAESTHESIA. Chloroform may be given internally in doses of from one to five drops. The British Pharmacopoeia contains a watery solution —the Aqua Chloro f ormi—which is useful in disguising the taste of nauseous drugs ; a liniment which consists of equal parts of camphor liniment and chloroform, and is a useful counter-irritant; the Spiritus Claloro f ormi (erroneously known as "chloric ether"), which is a useful anodyne in doses of from five to forty drops; and the Tinctura Chlorof ormi et Morpliinae Composita, which is the equivalent of a proprietary drug called chlorodyne. This tinc ture contains chloroform, morphine and prussic acid, and must be used with the greatest care.
Externally chloroform is an antiseptic, a local anaesthetic if allowed to evaporate, and a rubefacient, causing the vessels of the skin to dilate, if rubbed in. Its action on the stomach is practically identical with that of alcohol (q.v.), though in very much smaller doses. Chloroform is also used as a counter-irri tant; as a local anaesthetic for toothache due to caries; an anti spasmodic in tetanus and hydrophobia ; and as the best and most immediate and effective antidote in cases of strychnine poisoning.
BIBLIOGRAPHY.-W. H. Martindale and W. W. Westcott, The Extra Bibliography.-W. H. Martindale and W. W. Westcott, The Extra Pharmacopoeia (1924) ; W. E. Dinn, Manual of Pharmacology (1925).