Alkalies, or Alkaline salts: substan-ces of a very pungent taste; dissoluble in cold water; changing the colours of the blue flowers of vegetables to a green; destroying the acidity of four liquors, and forming with the acid a neutral compound; precipitating earthy bodies dissolved in acids (a); producing no precipitation or turbidness in solutions of the lixivial salts of vegetables. These lixivial salts are themselves alkalies: and to mingle uniformly with these bodies of their own kind, in a liquid state, is the most commodious and sure mark I can recollect, for distinguishing alkalies, universally, from certain solutions of earthy bodies in acids; some of which have, in a greater or less degree, all the common characters of alkalicity; but on being examined by this criterion, readily betray their composition, by rendering the limpid lixivial liquor milky, and depositing their earth; the acid, which before held the earth dissolved, being absorbed from it by the lixivial salt.

I. Sal alkalinus fixus. Fixt alkaline or lixivial salt: obtained from the ashes of vegetables, by macerating or boiling them in water, and afterwards evaporating the lye till the salt remains dry. It is fixt and fusible in the fire* (b), deliquiates in a moist air, dissolves in equal

(a) To this character of alkalicity there is one exception Or limitation. Volatile alkaline spirits made completely caustic by quicklime, on being mixed with a solution of calcareous earth in the nitrous or marine acids, occasion no precipitation or cloudiness. If the mixture be exposed for some time to the air, the alkaline spirit gradually loses its causticity; and then precipitates the earth: on blowing into it air from the lungs, through a glass pipe, the precipitation began immediately.

* (b) If in fusion a coal falls in, the alkali is resolved into dense white fumes, which act prodigiously on the brain and nervous system, rendering the head weak and benumbed, as in convalescence from some great disease, occasioning impatience and inquietude in every member. Beaume, its weight or less of water, and does not assume a crystalline form (a).

Fixt alkaline salts have an acrid fiery taste, and leave in the mouth a kind of urinous flavour. Saturated solutions of them in water corrode the solid parts of animals, dissolve fats and oils into saponaceous compounds, and liquefy almost all the animal humours, except perhaps only milk, which, when heated, they coagulate. Diluted largely with water, and drank warm in bed, they generally excite sweat: if that evacuation is not favoured by external warmth, they operate chiefly by urine, of which, in many cases, as in maniacal and hydropic ones, they frequently procure a copious and salutary discharge: they likewise loosen the belly, and in costive habits, where the direct purgatives or laxatives give only temporary relief, they render the benefit more lading. They seem in general to act by stimulating and deterging the solids, and resolving the viscidities of the humours; and by these means opening obstructions, or promoting secretion, in all the organs through which they pass. The dose is from two or three grains to fifteen or twenty; in some cases it has been extended to a dram. That they may be given, and continued for some time, with safety, in very considerable doses, appears from the experience of those, who have taken the strong solution of them called soap-lyes for the relief of calculous complaints.

(a) Though these salts, as commonly prepared, are never found to shoot into crystals, they do crystallize in part when solutions of them have been exposed for a length of time to the open air. The crystals are far milder in taste, and effervefce more strongly with acids, than the alkali in its common state.

U3 In putrid disorders, and a colliquated state of the humours, these salts have been generally, and I think justly, condemned: for though they have lately been discovered to resist putrefaction both in the fluids and solids of dead animals, yet in living ones they apparently increase the colliquation, with which all putrid diseases arc accompanied.

Fixt alkaline salts are obtainable, in greater or less quantity, from almost all vegetables; excepting perhaps only a few of the volatile acrid kind, as mustard seed. The salts of different plants, in the state wherein they are first extracted from the ashes, are found to differ in degree of strength, and in some other respects, from one another; many of them containing a portion, and some a very considerable one, of neutral salts of the vitriolic or marine kind (a). Purified by calcination, so as that all remains of the oil of the vegetable may be burnt out; and by deliquiation

(a) The readiest way of discovering neutral salt in the lixivial salts of vegetables is, by shaking a strong solution of them in a vial with about an equal quantity of rectified spirit of wine. If the salt is purely alkaline, the two liquors, on Handing for a moment, will separate from one another; the spirit rising to the top, and the alkaline solution collecting itself at the bottom, both of them transparent as at first. If neutral salts are mixed with the alkali, though in very small proportion, the spirit produces instantly an opake milkiness in the lye; and on Handing for a few minutes, a saline matter separates and falls to the bottom, in greater or less quantity, according as the alkali has a greater or less admixture of the neutral salt.

The exact quantity of pure alkali in any kind of lixivial salt or potash may be determined by means of acids. Some alkaline salt known to be pure, as good salt of tartar, is to be melted in an iron ladle, that all remains of watery moisture may be expelled: a certain quantity of this salt, as a dram, weighed out while warm, is to be dissolved in a little deliquiation in the air, by which only the alkali dissolves; they are all, except those of some marine plants (see Natron), so much alike, as not to be distinguishable, by any known method of trial, from one another.