In estimating the strength of alkali it has been usual to add the muriatic acid, and for each dram saturated, so many one-sixteenths of pure alkali were allowed. Alkalis, when pure, from whatever plants obtained, are entirely the same. What was, however, formerly styled pure alkali, is not so in the modern acceptation of the term. Mild alkalis are carbonated,; that is, neutralised by carbonic acid. When exposed to heat, or combined with quick lime, which has a greater affinity for the carbonic acid than alkali, they become what been styled caustic: in reality they are pure; and, when a mild alkali is united with a stronger acid, the separation of the carbonic acid, in the form of gas, occasions the effervescence. As a medicine, if largely diluted with water, and taken in bed or a warm room, vegetable fixed alkali promotes perspiration; but its tendency is more directly to become diuretic, and this is promoted by the patient resting in a cool situation. In this way it appears sometimes slightly laxative; and is useful to the studious, in whose stomachs acids usually abound. It destroys acidity in the primae viae, converting them into a mild aperient salt, and thus removes a cause of many chronical diseases. It loosens the texture of calcareous concretions by strongly attracting their air; and when pure, this power is increased. In those flatulent disorders which arise from a defective bile, it affords great relief.

The dose may be from gr. ij. to Э j. twice a day, but always plentifully diluted; the dose of Э j. should be mixed with at least x. of water. Considerable doses may be long continued, as is evident in those who take the aqua kali puri to remove calculous complaints; but the tone of the stomach, and' the powers of digestion, are sometimes destroyed by large doses and long use. It was supposed that alkalis thinned the blood; and numerous are the diseases attributed by the humoral pathologists to alkaline acrimony. It has indeed been suspected in scurvy, but seems to take place only in a small degree; and the alkali is the volatile in the form of an ammoniacal neutral. Fixed alkalis have been generally found diuretic; and perhaps in a greater degree when not neutralised in the stomach, or when defended from its acid by bitters. On the contrary, they are laxative only when they meet with such an acid as the stomach affords. The absence of an acid also seems necessary to their operation, as lithontriptics.

The fixed alkalis have lately been recommended in cutaneous complaints, and have been employed with some success. It is probable, however, that they chiefly act by correcting an acidity in the stomach, which occasions them; or by the discharge of urine which they excite. It is singular that acids have a similar power; nor does the distinction of the species adapted to each appear in any medical author. In general, the acids seem best adapted to the cases where the eruptions Occur in worn-out constitutions, and are of the tettery kind: the alkalis in the drier, scurfy eruptions. Yet even this distinction will not hold in every instance; nor indeed in our hands have the alkalis been eminently successful.

The fixed alkali has been sometimes thought useful in adding to the power of different menstrua, or in correcting the drastic acrimony of some resinous purgatives. With bitters, it has been supposed to be a febrifuge; and with camomile flowers, it has been in high esteem as a remedy for intcrmittents. It seems to produce some chemical change on bitters, as it reddens the infusions of bark and of rhubarb: and in many cases of dyspepsia appears an useful addition to astringents or tonics.

Externally, it is used in the form of a lotion in rachitic cases, as a stimulus in indolent ulcers, and in some cutaneous eruptions. The solution soon abates the pain arising from the stings of bees and wasps, and has been applied in burns. With sulphur, under the title of hepar sulphuris, it is also often useful. See Kali sulphuhatum.

The fixed alkalis have obtained a variety of appellations, partly from fancy, but more frequently from the-' ignorance of chemists; who, having obtained these salts from different sources, supposed that they had discovered a new substance.

The fixed vegetable alkali has been styled Cineres Russici and clavellati,fiot blanch, and pearl-ashes, alkahest glauberi marcoft,cendres grave/lees, sal tartari,sal absynthii nitrum fixum, cassob and lapis infernalis. It has been more lately styled by Dr. Black, lixiva; by the French chemists, potassa; by the London College, kali by others, oleum tartari and lixiva tartari.

The fixed mineral alkali has been styled by Dr. Black, irona,from a district of Tripoli where it abounds; soda, by the French chemists and the Edinburgh college, &x. Anatron, also called nataron, anachron, soude blanche, nitrum antiquorum, litron, aphronitum, baurach, sal alkalinus salis marini, barilla, soda, salitron, bariglia; anatron, anatrum.

Alcali volatile. Ammonia, called also Asa-nan. Volatile alkaline salt is either in a dry or liquid form; when dry, it is called salt; when liquid, water; the salt is obtained by sublimation, the water by distillation.

The volatile alkaline salt hath been chiefly obtained from the horns of deer, by distilling them in large iron pots, with a fire gradually increased to a strong red heat; but a similar salt, liquor, and oil, may be extracted from all animal substances except fat, from blood dried by a gentle heat, from urine first evaporated to the consistence of honey, and subjected to putrefaction. Urine, distilled with the addition of quick lime, yields an extremely pungent spirit. Ivory, and the bones of animals, are used for this purpose; bones are, indeed, preferable to hartshorn; as the salt and spirit of bones require less rectification, are less disgustful to the stomach-, and the spirit retains its limpid appearance longer than that from horns: when bones are used, their fat must be extracted first by long boiling. Wood-soot affords a salt liquor and oil, not differing from those of hartshorn, except as it is less easy to rectify. From crude sal ammoniac, mixed with any fixed alkaline substance, the volatile alkaline salt of the sal ammoniac is obtained, and with very little trouble rendered perfectly pure; the spirit of sal ammoniac is free from the inconveniences which attend those spirits obtained from horns, ivory, bones, etc.