The action of the strong acids on alcohol aided by heat, produces an order of compounds which possess both important chymical properties and medicinal virtues. These are named Aethers, and agree in certain general properties, but vary in some of their qualities, and in their formation, according as they are produced from different acids; and they are distinguished by the name of the acid with which they are prepared. They are all extremely volatile, and require to be preserved in closely stopped phials.1 The following are medicinally used.

Aether Sulphuricus. Lond. Sulphuric Aether

"Take of rectified spirit, three pounds; sulphuric acid, two pounds; carbonate of potassa, previously ignited, one ounce. Pour two pounds of the spirit into a glass retort, and having added the acid, mix. Then place it on a sand-bath, so that the liquor may boil as quickly as possible, and the aether pass into a receiver, kept cool by ice or water. Let the liquor distil until a heavier fluid begin to pass over. Having lowered the heat, pour the remainder of the spirit on the liquor, which remains in the retort, that aether may distil as before. Mix the distilled liquors together, then pour off the supernatant portion, and add to it the carbonate of potassa, agitating occasionally for an hour. Finally, distil the aether from a large retort, and keep it in a closely-stopped bottle.

1 The phial proposed by Dr. Dewar is the best for this purpose. It consists of a stopped phial, having a circular rim round its shoulder, not rising quite so high as the mouth of the bottle, and a glass cup with a heavy bottom, which, when inverted over the mouth of the phial, and mercury poured into the rim, hermetically closes it. Annals of Phil, vol. x. p. 20.

Edinburgh,

"Take of sulphuric acid, alcohol, of each thirty-two ounces. Pour the alcohol into a glass retort, capable of sustaining a sudden heat; then pour the acid on it in an uninterrupted stream. Mix them gradually by frequent and gentle agitation : then immediately distil from a sand-bath, previously heated for the purpose, into a receiver kept cold with water or snow. Let the fire be so regulated that the fluid may boil as soon as possible, and continue to boil until sixteen ounces shall have distilled over: then let the retort be removed from the sand-bath.

"To the distilled liquor, add two drachms of potassa; then distil again from a high retort, with a very gentle heat, into a receiver kept cold, until ten ounces have passed over.

"If sixteen ounces of alcohol be added to the residuary acid after the first distillation, and the distillation repeated, aether will be reproduced. And this may be often repeated."

Liquor Aethereus Sulphuricus. Dub. Sulphuric Aethereal Liquor

"Take of rectified spirit, sulphuric acid, each thirty-two ounces, by weight. Pour the spirit into a glass retort, fit to bear a sudden heat, and over it the acid in a continued stream. Mix, and distil into a cold receiver twenty ounces, by measure, of the liquor, by the aid of a suddenly raised strong heat.

"To the residue in the retort add sixteen ounces of rectified spirit, and by distilling again, more aethereal liquor will be produced."

Aether sulphuricus, Dub. Sulphuric Aether.

"Take of sulphuric aethereal liquor, twenty fluid ounces; subcarbonate of potassa, dried and in powder, two drachms. Mix them, and distil from a high retort by means of a very gentle heat, into a receiver kept cold, twelve fluid ounces. The specific gravity of this fluid is to that of distilled water as 765 to 1000."

Syn. Ether (F.), Schwefeliitther (G.), Etere (I).

The admixture of alcohol and sulphuric acid produces an almost instantaneous formation of aether, which is made sensible by the odour of the mixture; while by the mutual action of the spirit and the acid on each other a considerable evolution of caloric takes place, and the temperature of the mixture is raised to 180°. Whatever can encourage the sudden rise of temperature, and the disengagement of aethereal vapours before the apparatus be adjusted, should be avoided; for not only is the retort in danger of being broken, but a considerable waste of product also takes place. The retort should be thin, and the sand-bath previously heated to more than 200°; for unless the liquor boil immediately alcohol only is given over: as soon as boiling commences the aether is formed, and distils over. The aether, as it distils, is condensed in the cool receiver, in the form of a colourless, limpid, transparent fluid; but towards the end of the operation, a white vapour also comes over, on the appearance of which the distillation should be stopped, or the receiver changed. The receiver ought to be ample, and kept cool with ice or snow, or cold water, which we have found to be preferable to ice or snow.

The best mode of applying it is to lay narrow shreds of woollen cloth over the receivers, with one end of each immersed in a vessel of cold water placed higher than the receiver, by which means the water is made to trickle constantly over it; and by the evaporation the receiver is kept in a sufficiently low temperature, and at the same time the nature of its contents is distinctly seen, which cannot be conveniently done when they are immersed in snow, or ice, or even in water. The luting, which answers best in this operation, is common paste, spread on slips of calico, which are to be first applied, and when dry surrounded with pieces of wet bladder.

The product of the first distillation is sulphuric aether combined with water, alcohol, and a small portion of sulphurous acid, forming an impure aether of the specific gravity .768; and that of the second distillation, or that obtained after the addition of a new portion of alcohol, is a similar aether of the specific gravity .807: on mixing these, a fluid of the specific gravity .788 is obtained, which is unrectified aether. By the rectification of this aether according to the directions of the British Colleges, it is deprived of the sulphurous acid and nearly of all the water, and its specific gravity is reduced to .732, or, when highly rectified, to .725; but it still contains some water and alcohol, as aether of a specific gravity so low as .632 in the temperature of 60° is said to have been obtained.1 The use of the alkali in the rectification is to separate and detain the acid and the water by its affinity for these substances; and this is still more completely accomplished by the addition of a portion of black oxide of manganese, which, by affording oxygen to the sulphurous acid, converts it into sulphuric acid, and thus renders it perfectly fixed at the temperature employed.