1911 Encyclopædia Britannica/Chloroform
CHLOROFORM (trichlor-methane), CHCl3, a valuable anaesthetic, a colourless liquid, possessing an agreeable smell and a pleasant taste. It may be prepared by the action of bleaching powder on many carbon compounds, such, for example, as ethyl alcohol and acetone (E. Soubeiran, Ann. chim. phys., 1831 , 48, p. 131; J.v. Liebig, Ann., 1832, I, p. 199), by heating chloral with alkalis (Liebig), CCl3CHO + NaHO = CHCl3 + NaHCO2, or by heating trichloracetic acid with ammonia (J. Dumas, Ann., 1839, 32, p. 113). In the preparation of chloroform 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 (0°/4°) (T. E. Thorpe). It is an exceedingly good solvent, especially for fats, alkaloids and iodine. It is not inflammable. The vapour of chloroform when passed through a red-hot tube yields hexachlorbenzene C6Cl6, perchlorethane C2Cl6, and some perchlorethylene C2Cl4 (W. Ramsay and S. Young, Jahresberichte, 1886, p. 628). Chromic acid converts it into phosgene (carbonyl chloride, COCl2). It reacts with sodium ethylate to form ortho-formic ester, CH(OC2H5)3, and when heated with aqueous ammonia for some hours at 200-220° C. gives carbon monoxide and ammonium formate, 2CHCl3 + 7NH3 + 3H2O = NH4·HCO2 + CO + 6NH4Cl (G. André, Jahresb., 1886, p. 627). When digested with phenols and caustic soda it forms oxyaldehydes (K. Reimer, Ber., 1876, 9, p. 423); and when heated with alcoholic potash it is converted into potassium formate, CHCl3 + 4KHO = KHCO2 + 3KCl + 2H2O. It combines with acetoacetic ester to form the aromatic compound meta-oxyuvitic acid, C6H2·CH3·OH·(COOH)2. A hydrate, of composition CHCl3·18H2O, has been described (G. Chancel, Fresenius Zeitschrift f. anal. Chemie, 1886, 25, p. 118); it forms hexagonal crystals which melt at 1·6° C.
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, phenyl isocyanide (recognized by its nauseating smell) is produced,
For the action and 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 Chloroformi—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 Chloroformi (erroneously known as “chloric ether”), which is a useful anodyne in doses of from five to forty drops; and the Tinctura Chloroformi et Morphinae Composita, which is the equivalent of a proprietary drug called chlorodyne. This tincture 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. The uses of chloroform which fall to be mentioned here are:—as a counter-irritant; as a local anaesthetic for toothache due to caries, it being applied on a cotton-wool plug which is inserted into the carious cavity; as an antispasmodic in tetanus and hydrophobia; and as the best and most immediate and effective antidote in cases of strychnine poisoning.