Crystallized Tartar acts also upon several other metallic substances: for instance, it dissolves the Regulus, Liver, and Glass of Antimony, and thence acquires an emetic quality: it is then called _Stibiated_ or _Emetic Tartar_. It likewise dissolves Lead, and therewith forms a salt which, in the figure of its crystals, resembles Tartarised Tartar. It is very extraordinary that Tartar, which of itself is not soluble in water, should be soluble therein when become a neutral salt by uniting either with alkalis or with absorbent earths, or even with metals. With respect to alkalis, indeed, it may be urged, that, having themselves a great affinity with water, they communicate to Tartar some of that facility with which they naturally unite therewith: but the same cannot be alledged concerning absorbent earths, and metallic substances, which water dissolves not at all, or at least with great difficulty, and in small quantity. This effect, therefore, must be attributed wholly to some change in the disposition of its parts which is to us unknown. All the Soluble Tartars are easily decompounded by exposing them to a certain degree of heat. In distillation they yield the same principles which are obtained from Tartar; and what remains fixed in the fire, after they are thoroughly burnt, is a compound of the alkali which Tartar naturally produces, and of the alkaline or metallic substance with which it was converted into a neutral salt. As Crystal of Tartar is the weakest of all acids, on account of the oily and earthy matters with which it is combined, Soluble Tartars are decompounded by all the acids; by any of which crystal of Tartar may be separated from the substance that serves it for a basis and renders it a neutral salt. The other acids which are procured from vegetables, and even those which are obtainable from some animal substances, may all be referred to and compared with either Vinegar or Tartar, according to the quantities of oil or earth with which they are combined. After all, these acids have not yet been thoroughly examined. There is great reason to think that they are no other than the mineral acids, which, in passing through the bodies of vegetables, and even of animals, undergo a considerable change, especially by contracting an union with oily matters. For, as we said before in treating of Vinegar, by freeing them from their oil they are brought very near to the nature of mineral acids; and so likewise the mineral acids acquire many of the properties of vegetable acids by being combined with oils. CHAP. XV. _Of the_ PUTRID FERMENTATION, _or_ PUTREFACTION. Every body which hath gone through the two stages of fermentation above described, that is, the spirituous and the acetous fermentation, being left to itself in a due degree of warmth, which varies according to the subject, advances to the last stage of fermentation; that is, to putrefaction.