It will be shewn in its proper place, that almost every vegetable matter, as well as Tartar, leaves a fixed alkali in its ashes: yet Tartar has these peculiar properties; first, it assumes an alkaline character even when burnt or calcined in close vessels, whereas other substances acquire it only by being burnt in the open air; secondly, the alkali of Tartar is stronger and more saline than almost any that is obtained from other matters. This alkali, when thoroughly calcined, powerfully attracts the moisture of the air, and melts into an unctuous alkaline liquor, improperly called _Oil of Tartar per deliquium_. This is the alkali generally used in making the _Terra Foliata_, mentioned under the head of Vinegar; for which reason this combination is called _Terra Foliata Tartari_; a name suitable enough. But the same cannot be said of the other name, _Regenerated Tartar_, which is also given it. It is true, that on this occasion an oily acid is restored to the earth of the Tartar, analagous to that of which the fire had deprived it: but the compound thence resulting is a neutral salt which very readily dissolves in water; whereas Tartar is manifestly acid, and not soluble, or at least hardly soluble, in water. Crystals of Tartar combined with alkali of Tartar produce a great effervescence while they are mixing, as all acids usually do; and if the combination be brought exactly up to the point of saturation, a perfectly neutral salt is formed, which shoots into crystals, and easily dissolves in water; and this hath procured it the name of _Soluble Tartar_. It is also called the _Vegetable Salt_, as being obtained from vegetables only; and again, _Tartarised Tartar_, because it consists of the acid and the alkali of Tartar combined together. Crystals of Tartar combined with alkalis procured from the ashes of maritime plants, such as Soda, which alkalis resemble the basis of sea-salt, form likewise a neutral salt, which crystallizes well, and dissolves easily in water. This salt is another sort of soluble Tartar. It is called _Saignette's Salt_, from the inventor's name. Both the Vegetable Salt and Saignette's Salt are gently purgative soaps, and much used in Medicine. Tartar likewise dissolves the absorbent earths, as lime, chalk, _&c._ and with them forms neutral salts which are soluble in water[3]. It even attacks metallic bodies, and when combined with them becomes soluble. A soluble Tartar for medical use is prepared with Crystals of Tartar and Iron: the metallic salt thereby produced hath the name of _Chalybeated Soluble Tartar_. This salt attracts the moisture of the air, and is one of those which do not crystallize. [3] See Mr. Duhamel's Essays on this subject in the Memoirs of the Academy of Sciences.