Or Alkali, (of al and kali, i. e. the essence or the. whole of kali, the plant from which it was originally prepared, though now derived from plants of every kind). Alkaline salt is called alafi, alafor, alafort, and calcadis. As alkalis effervesce with acids, all volatile or fixed salts, and all terrestrious matters which ferment with acids, are called alkalis.

Alkalis are mineral, vegetable, and animal, which three were particularly distinguished by the term, adding to it the peculiar epithet; but the College of Physicians of London have now distinguished them by three different appellations; calling them natron, kali, and ammonia; but they are either earthy or saline..

The former terms are now indeed found to be peculiarly improper; since the kali is discovered in some minerals, even in some granites, and the ammonia is obtained not only from plants, but seeds. The soda or natron occurs both in vegetables and animals. Besides these, there are several earths, which, in their more general properties, resemble alkalis; particularly lime, magnesia, barytes, and strontian.

Earthy alkalis are those substances which of themselves scarcely dissolve in pure water; but if added to acids, form a neutral. Of this sort are chalk, limestone, crabs'-eyes,oyster-shells,egg-shells, etc. Thus, if pure water is acidulated with oil of vitriol, it effervesces, if you scrape chalk into it; and during the effervescence, the water hath a brisk taste; when enough of chalk is added, the acidity is lost.

Their taste is in general acrid and urinous; they change the blue colours of vegetables to a green, destroy the taste and other properties of acids, and dissolve with peculiar facility in water. As the volatile alkali is known to be a compound of azote and hydrogen, it is probable that the fixed kinds are formed of similar ingredients. Thus hydrogen, with lime, may form pot-ash; with magnesia,soda. Some experiments supposed to prove these combinations, have been found fallacious; yet the principle is highly probable.

The saline alkalis are fixed and volatile. The latter of which differs from the former only in volatility and its consequence; the volatile alkali rises sooner than the rectified spirit of wine.

Tachenius is said to have first made the fixed vegetable alkali: he established the general use, but it was known long before his time. A fixed alkali is the basis of sea salt.

------ vegetabile. This was formerly prepared from wormwood, and named sal absinthii; but the College of Physicians have supplied its place with the kali preparatum, which is made in the usual method of dissolving, filtering and crystallising the salts of vegetable. The same salt may be prepared from tartap, burnt till it becomes of an ash colour: and, indeed, of all the substances from which a fixed alkaline salt is obtained, tartar yields the largest quantity, and with the least trouble. The college has ordered the solution of potash to be set apart a whole night for the neutral salts, which are part of the composition, to crystallise, but that is not sufficient; for, in order to have the alkali in its purest state freed from those salts, which is their intent, the solution will require to be exposed to crystallisation three times, at least: otherwise it will retain too great a share of vitriolated tartar. Observations on the Pharmacopaia Collegii Regalis, etc. London, 1788.

The quantity of pure potash usually employed in commerce, is estimated by Vauquelin according to the following table:

Alcali minerale. This mineral fixed alkaline salt may be procured from sea salt, and from the waters of many springs, either by distillation of the acid, or the superior affinity of the vegetable fixed alkali. This alkali differs from that of vegetables, by being milder, and less acrid to_the taste; melting more easily |n the fire; requiring more water to dissolve it; in its concreting into crystalline masses on evaporation after solution in water; not becoming liquid by exposure to the air; and in being a less powerful solvent of the stone in the bladder. As a less deliquescent salt, it is best adapted to form pills. The crystals are prismatic, resembling those of the natron vitriolatum. With this mineral alkali the Spanish soap is made. This salt, joined with the vitriolic acid, forms the natron vitrio-latim; with the nitrous, nitrum cubicum; with the muriatic, sea' salt; and with vegetable acid, the natron tartarisatum. The Egyptian soda was usually reckoned the strongest; but it is usually mixed with sea salt, with sand and a kind of steatite; then the Spanish (barilla). After this came the trona from Tripoli, and then that prepared from different species of kelp. We have now, however, an ample supply from another source. In preparing the oxygenated muriatic for the purposes of bleaching, the muriate of soda is decomposed by the sulphuric acid. The sulphate of soda is afterwards decomposed in different ways; for which see Accum's Chemistry.

-------------vegetabile. The vegetable alkali, or potash, and the mineral alkali, or soda, possess the general properties of alkalis; and most inflammable substances are acted upon by them. They melt in a moderate heat; and in a stronger they are volatilised: in the dry way they dissolve earths and the calces of metals.

Fixed alkaline salt is obtainable from sea salt and nitre, and from all vegetables, except perhaps some of the volatile acrid kind, which impress the nose sharply with their scent, such as mustard seed, garlic, etc.; these contain parts that are volatile, and become volatile salt. The fixed salt of some plants vary greatly from one another in strength, etc. if taken in the state wherein they are first extracted from the ashes: they sometimes contain some neutral salt of the vitriolic or of the muriatic kind, which are discovered by shaking them in a vial, with equal part of spirit of wine, the fluid with neutral salt becomes milky. Sometimes a bitter crystalline hard salt, that is neither acid nor alkaline, but a mixture of earthy and alkaline neutrals, is found among the fixed alkaline salt; readily separated by means of cold water, in which it will not dissolve. This hard salt is never met with in making the salt of tartar, but in potash it is often found. The salts of the leaves, and other herbaceous parts of plants, are more difficultly brought to a state of purity than those of the more woody and compact portions, a portion of the oil being so tenaciously retained: some endeavour to retain this oil in the salt, by burning the vegetables in a smothering heat until they are reduced to ashes. They do this to render the salt more mild, or to combine the virtues of the oil; but the mineral alkali is sufficiently free from acrimony to.sit easy on the most irritable stomach, when administered in the usual modes; and the empyreumatic oil, retained, will occasionally, it is supposed, excite nausea. To this, however, there are objections. Some practitioners have thought that saline draughts made from the alkali, which still retained a portion of the oil of wormwood, sat more easily on the stomach: we are confident that the taste was more pleasing. In other instances, the advantages are less equivocal: we allude to the ashes of broom and tobacco, which certainly possess a stronger diuretic power from the oil adhering to the salts.