§ 171. Fatal Dose.—The fatal dose of ether, when taken as a liquid, is not known. 4 grms. (1·28 drms.) cause toxic symptoms, but the effect soon passes. Buchanan has seen a brandy-drinker consume 25 grms. (7 drms.) and yet survive. It is probable that most adults would be killed by a fluid ounce (28·4 c.c.).
§ 172. Ether as an Anæsthetic.—Ether is now much used as an anæsthetic, and generally in conjunction with chloroform. Anæsthesia by ether is said to compare favourably with that produced by chloroform. In 92,000 cases of operations performed under ether, the proportion dying from the effects of the anæsthetic was only ·3 per 10,000 (Morgan), while chloroform gives a higher number (see [p. 149]). The mortality in America, again, from a mixture of chloroform and ether in 11,000 cases is reckoned at 1·7 per 10,000; but this proportion is rather above some of the calculations relative to the mortality from pure chloroform, so that the question can hardly be considered settled. The symptoms of ether narcosis are very similar to those produced by chloroform. The chief point of difference appears to be its action on the heart. Ether, when first breathed, stimulates the heart’s action, and the after-depression that follows never reaches so high a grade as with chloroform. Ether is said to kill by paralysing the respiration, and in cases which end fatally the breathing is seen to stop suddenly: convulsions have not been noticed. The post-mortem appearances, as in the case of chloroform, are not characteristic.
§ 173. Separation of Ether from Organic Fluids, &c.—Despite the low boiling-point of ether, it is by no means easy to separate it from organic substances so as to recover the whole of the ether present. The best way is to place the matters in a flask connected with an ordinary Liebig’s condenser, the tube of the latter at its farther end fitting closely into the doubly perforated cork of a flask. Into the second perforation is adapted an upright tube about 2 feet long, which may be of small diameter, and must be surrounded by a freezing mixture of ice and salt. The upper end of this tube is closed by a thistle-head funnel with syphon, and in the bend of the syphon a little mercury serves as a valve. Heat is now applied to the flask by means of a water-bath, and continued for several hours; the liquid which has distilled over is then treated with dry calcic chloride and redistilled exactly in the same way. To this distillate again a similar process may be used, substituting dry potassic carbonate for the calcic chloride. It is only by operating on these principles that the expert can recover in an approximate state of anhydrous purity such a volatile liquid. Having thus obtained it pure, it may be identified (1) by its smell, (2) by its boiling-point, (3) by its inflammability, and (4) by its reducing chromic acid. The latter test may be applied to the vapour. An asbestos fibre is soaked in a mixture of strong sulphuric acid and potassic dichromate, and then placed in the tube connected with the flask—the ethereal (or alcoholic) vapour passing over the fibre, immediately reduces the chromic acid to chromic oxide, with the production of a green colour.
V.—Chloroform.
CHLOROFORM, TRICHLOROMETHANE OR METHENYL CHLORIDE (CHCl3).
§ 174. Chloroform appears to have been discovered independently by Soubeiran and Liebig, about 1830. It was first employed in medicine by Simpson, of Edinburgh, as an anæsthetic. Pure chloroform has a density of 1·491 at 17°, and boils at 60·8°; but commercial samples have gravities of from 1·47 to 1·491. It is a colourless liquid, strongly refracting light; it cannot be ignited by itself, but, when mixed with alcohol, burns with a smoky flame edged with green. Its odour is heavy, but rather pleasant; the taste is sweet and burning.
Chloroform sinks in water, and is only slightly soluble in that fluid (·44 in 100 c.c.), it is perfectly neutral in reaction, and very volatile. When rubbed on the skin, it should completely evaporate, leaving no odour. Pure absolute chloroform gives an opaline mixture if mixed with from 1 to 5 volumes of alcohol, but with any quantity above 5 volumes the mixture is clear; it mixes in all proportions with ether. Chloroform coagulates albumen, and is an excellent solvent for most organic bases—camphor, caoutchouc, amber, opal, and all common resins. It dissolves phosphorus and sulphur slightly—more freely iodine and bromine. It floats on hydric sulphate, which only attacks it at a boiling heat.
Chloroform is frequently impure from faulty manufacture or decomposition. The impurities to be sought are alcohol, methylated chloroform,[158] dichloride of ethylene (C2H4Cl2), chloride of ethyl (C2H5Cl), aldehyde, chlorine, hydrochloric, hypochlorous, and traces of sulphuric acid: there have also been found chlorinated oils. One of the best tests for contamination by alcohol, wood spirit, or ether, is that known as Roussin’s; dinitrosulphide of iron[159] is added to chloroform. If it contain any of these impurities, it acquires a dark colour, but if pure, remains bright and colourless.