There are several sorts of Salts, differing from one another, in respect either of the quantity, or the quality of the earth in their composition; or, lastly, they differ on account of some additional principles, which not being combined with them in sufficient quantity to hinder their Saline properties from appearing, permit them to retain the name of Salts, though they render them very different from the simplest Saline Substances. It is easy to infer, from what has been said of Salts in general, that some of them must be more, some less, fixed or volatile than others, and some more, some less, disposed to unite with water, with earth, or with particular sorts of earth, according to the nature or the proportion of their principles. Before we proceed further, it is proper just to mention the principle reasons, which induce us to think that every Saline Substance is actually a combination of earth and water, as we supposed at our entering on this subject. The first is, the conformity Salts have with earth and water, or the properties they possess in common with both. Of these properties we shall treat fully, as occasion offers to consider them, in examining the several sorts of Salts. The second is, that all Salts may be actually resolved into earth and water by sundry processes; particularly by repeated dissolution in water, evaporation, desiccation, and calcination. Indeed the Chymists have not yet been able to procure a Saline Substance, by combining earth and water together. This favours a suspicion, that, besides these two, there is some other principle in the composition of salts, which escapes our researches, because we cannot preserve it when we decompose them; but it is sufficient to our purpose, that water and earth are demonstrably amongst the real principles of Saline Substances, and that no experiment hath ever shewn us any other. SECTION I. _Of_ ACIDS. Of all Saline Substances, the simplest is that called an _Acid_, on account of its taste; which is like that of verjuice, sorrel, vinegar, and other sour things, which, for the same reason, are also called Acids. By this peculiar taste are Acids chiefly known. They have moreover the property of turning all the blue and violet colours of vegetables red, which distinguishes them from all other salts.