The volatile alkalies obtained from different substances appear, like the fixt, to be, in their state of perfect purity, one and the same thing. But as first distilled from the subject, they are largely impregnated with its oil rendered fetid or empyreumatic by the process in which the salt was generated; and as these oils differ from one another in degree of subtility and fetidness, the salts partake of the same differences, till repeated distillations or other processes have either separated the adhering oils, or subtilized and purified them to the same degree. By repeated distillations, all animal oils become limpid as water, lose their fetor, acquire a penetrating fragrant smell, and a gratefully pungent taste: thus rectified, they are said, by Dippelius, Hoffman, and others, to act, in doles of half a drop, as diaphoretics, anodynes, and antispasmodics. The volatile alkalies used in medicine are expected to be either pure from oil, or to have their oil in this subtilized state.

The oily volatile alkalies have been chiefly prepared from hartshorn, by distillation in large iron pots, with a fire increased by degrees to a strong red heat. At first there arises an aqueous liquor, then the volatile salt, along with a yellowish and at length a dark reddish oil: if the aqueous liquor is not removed before the salt begins to come over, a part of the salt dissolves in it, and thus forms what is called spirit.

(a) See Huxham's Dissertation on the malignant sore throat.

Oleum animate vulgo.

The oil, excepting so much of it as is incorporated with the alkali, may be separated from the spirit by filtration through wetted paper, which transmits the spirit and retains the oil. The salt and spirit are then distilled again together, with a very gentle heat, in a glass retort; and the distillation carefully repeated several times, till the salt becomes exceedingly white, and the spirit limpid as water,, and of a grateful smell. The salt becomes the sooner pure, if it be separated from the spirit, and sublimed first from an equal weight of pure chalk and afterwards from a little rectified spirit of wine. If the whole of the volatile salt is required in a solid form, it may be recovered from the spirit by sublimation in a tall narrow cucurbit, the salt rising into the head, while the watery fluid remains behind. In all the distillations of the spirit, greatest part of the salt comes over before the phlegm; and the process should be continued no longer than till so much of the phlegm has followed as is nearly sufficient to dissolve it; that a part of the salt remaining undissolved may be a criterion, to the purchaser, of the saturation or strength of the spirit. - A spirit, salt, and oil, are sometimes distilled in the same manner from wood foot, but here more labour is required to render the salt and spirit pure.

Liquor vola-tilis, fal, & oleum cornu cervi Ph. Lond.

Though the whiteness and limpidity which the salts and spirits of hartshorn, soot, and other like substances, acquire by the above methods of purification, seem to shew that they are diverted of oil; they are nevertheless found to participate still of that principle in no small degree. In long keeping they contract a yellow colour, and at length become again nauseous and foetid; the oil seeming to be more and more extricated, or to lose by degrees of the subtility and grate-fulness which it received from the rectification. The oftener the distillation is repeated, the more permanent is the subtilization of the oil.

The most effectual purification of these salts is obtained, by combining them with mineral acids, and afterwards separating the acid. It is not needful to make such a combination on pur-pose: for such a one is produced more com-pendiously, in the way of trade, and called in the shops sal ammoniac: see the following article.

If sal ammoniac be mingled with any fixt alkaline salt, either in. the form of powder or so-lution, its acid will be absorbed by the fixt alkali; and the volatile alkali, thus set at liberty again, will immediately discover itself by its pungent odour, and may be collected perfectly pure by distillation. Eighteen ounces of fixt alkali, and one pound of sal ammoniac, may be distilled with four pints of water in a gentle heat, till two pints are drawn off†: or sixteen ounces each of the two salts may be distilled with two pounds of water, to dryness‡. The volatile alkaline salt may be extricated likewise by means of chalk, but with this difference, that the chalk does not begin to act upon the sal ammoniac, or absorb its acid, till the mixture is considerably heated: one part of the salammoniac may be mixed with two of chalk, and the mixture set to sublime in a retort with a strong fire.

Aqua ammo-niae Ph. Lond. Spirit. sal. ammoniac. ‡ Ph Ed.

Quicklime, which heightens the pungency of fixt alkalies even to causticity, has a like effect upon the volatile: it renders the fixt more easily liquefiable, and the volatile permanently liquid, preventing their concretion into a solid form: the volatile alkali, like the fixt, in having its activity thus increased by quicklime, loses its power of effervescing with acids; from whence it may be presumed, that the lime acts, on one alkali as on the other, by absorbing their air ("see page 255). This pungent volatile spirit may be prepared, by flaking two pounds of quicklime in two pints of water, letting it stand an hour, and then adding a pound of powdered sal ammoniac with six pints of warm water: immediately adapt a recipient, (for the pungent vapours begin to arise on the first contact) and with a gentle heat draw off one pint. *Or two pounds of quicklime may be flaked with one pound of water, and covered till it falls to a powder, which is then to be put in a retort with sixteen ounces of sal ammoniac dissolved in four times its weight of water. The vessels are to be very carefully luted, and with a very gentle heat twenty ounces are to be drawn off. This spirit is held too acrimonious for internal use, and has therefore been chiefly employed in smelling-bottles. It is an excellent menstruum for certain vegetable substances, as Peruvian bark, which the milder spirits extract little from; and when saturated with bodies of this kind, its pungency is so far sheathed, that it may be taken inwardly with as great safety as tinctures made in the other spirits. In long keeping, unless the bottle is quite full and very closely secured, it gradually imbibes air, as appears from the effervescence which it raises with acids; and loses proportion-ably of its pungency.