Chloroform, CHCl3, was discovered as a chemical curiosity about the same time (1831) by Guthrie in America, Liebig in Germany, and Soubeiran in France. Soon, however, its properties as a stimulant when taken internally attracted attention, and when in 1847 it was brought into prominent notice as an anæsthetic by Sir James Simpson, it was at once recognised as one of the most valuable contributions of chemical science to suffering humanity. See ANÆSTHESIA.
Chloroform is composed of 12 parts of carbon, 1 part of hydrogen, and 106½ parts of chlorine. It may be produced in several ways, but in this country at least the process by which it is obtained from bleaching powder is the only one adopted on the large scale. The materials employed are bleaching powder, alcohol, and water. The bleaching powder and water are mixed together to form a thin cream, the alcohol added, and the whole placed in a capacious still, connected with suitable condensing apparatus. On the application of heat the contents rapidly froth up, and even though the external application of heat be stopped, the chemical action is so violent that the chloroform distils over rapidly along with water and any excess of alcohol. As so obtained it is very impure, and requires to be carefully treated with sulphuric acid, and then redistilled before it is fit for anæsthetic purposes. Pure chloroform is a limpid, mobile, colourless, volatile liquid, with a characteristic odour, and a powerful sweetish taste. When diluted with alcohol it enters into the composition of artificial fruit-essences, to which it gives a flavour akin to that of ripe apples. It is a very heavy liquid, its specific gravity being about 1.500 (water = 1.000), and as it does not readily mix with or dissolve in water, it falls to the bottom when poured into a vessel of that liquid, forming a distinct layer. Chloroform is readily miscible with alcohol and ether, and it dissolves camphor, amber, gutta-percha, wax, black and red sealing-wax, iodine, and bromine, as well as strychnine and other alkaloids. It dissolves a small proportion of water, being also slightly soluble in that liquid. Chloroform is not combustible in the ordinary sense of the term, but when its vapour is brought in contact with flame it burns, imparting a green tint to it, and irritating fumes are produced. Pure chloroform is not met with in commerce owing to the readiness with which it decomposes when exposed to light. In order to prevent this a small proportion of alcohol is added, the specific gravity being thus reduced from 1.500 to 1.497. When evaporated on the hand no disagreeable odour should be noticeable, and when shaken with sulphuric acid only a very slight discoloration of the acid (due to the small proportion of alcohol) should result. Besides its anæsthetic properties, which are elsewhere discussed (see ANÆSTHESIA), chloroform is used in medicine both externally and internally. When applied to the skin or any of the mucous membranes it acts as a powerful irritant, producing a burning sensation, and on this account it is of value as an application in rheumatism, lumbago, and neuralgia. As an application to a decayed tooth its action is twofold, as a stimulant and counter-irritant locally, and also to a partial extent as an anæsthetic. Taken internally, diluted with alcohol, it is a powerful stimulant, and readily produces a species of intoxication. It is by some habitually taken as a narcotic luxury. As chloric ether, a product distilled from bleaching powder, and containing chloroform, it enters into the composition of cough mixtures, pick-me-ups, &c.