Natron, Anatron, Soude blanche, Pharm. Paris. Nitrum antiquorum. Aphronitrum. Bau-racb. Natron, or Mineral fixt alkaline salt: This salt is contained in great abundance in the waters of the ocean, and makes the balls of the neutral salt so plentifully extracted from them for alimentary uses. It is likewise disco-verable in sundry mineral springs, even of those which do not participate of sea salt. The celebrated Seltzer waters, in the archbifhoprick of Treves, appear to be no other than a dilute so-lution of this salt mixed with a little earthy matter: twelve ounces of the water, according to Hoffman's analysis, yield a scruple of the pure alkali. In some of the eastern countries it is found in considerable quantities on the surface of the earth, sometimes pure, but more commonly blended with various heterogeneous matters, from which it is extracted by means of water. I have been favoured by Dr. Heberden with a sample of this salt in a very pure state, which was taken up on the Pic of Teneriffe, and with which some parts of that mountain are covered. An account of this salt, as found fossil in a crystalline state, in the country of Tripoli, is contained in the Phil. Trans. vol. Ixi. part ii. The alkali called soda, or barilla, prepared by incinerating the maritime plant kali or glass-wort, contains a salt of the same kind. * This is received into the London catalogue of simples, and a purified salt is ordered to be prepared from it, by repeated solution in water, colature, and crystallization.

The mineral alkali agrees in its general qualities with the common lixivial salts of vegetables. The differences which have been ob-served are, that it is milder and less acrid in taste: that it melts easier in the fire, and requires more water for its solution: that when dissolved in water it concretes, on evaporation, into crystalline masses: that when exposed to a moist air, though it grows somewhat moist on the surface, it does not run into a liquid form: that in a dry air, the crystals lose the water ne-cessary for their crystalline form, and fall by degrees into a white powder: that the neutral salt, resulting from its coalition with the vitriolic acid, fal glauberi, is very easily dissoluble in water and fusible in the fire: that with the nitrous acid it forms cubical crystals, niirum cubi-cum; with the marine, perfect sea salt; with tartar, a salt which easily crystallizes, fal rupel-lense. Made caustic by lime, it proves greatly inferiour to the vegetable alkali in dissolving the urinary calculus (a).

Barilla Ph. Lond.

Natron prae-par. Ph. Lond.

This salt appears to possess the same general virtues with the vegetable alkalies; but as it does not liquefy in the air, it is better adapted for an ingredient in powders; and as it is less acrimonious, it may be presumed to be less dis-posed to stimulate the first paffages: some of the chemists have taken great pains, in the preparation of the common alkalies, to preserve in them a part of the oil of the plant, so as to reduce them to such a degree of mildness, as this alkali, with much greater uniformity and certainty, possesses in its pure state.