The general Plan on which I proceed is to suppose my Reader an absolute Novice in Chymistry; to lead him from the most simple truths, and such as imply the lowest degree of knowledge, to such as are more complex, and require a greater acquaintance with Nature. This order, which I have laid down for my rule, hath obliged me to begin with examining the most simple substances that we know, and which we consider as the elements whereof others are composed; as, by knowing the properties of these elementary parts, we are naturally led to those of their several combinations; and, on the other hand, in order to know the properties of compound bodies, it is necessary we should be first acquainted with the properties of their principles. The same reason induced me, when enquiring into the properties of one substance, to take no notice of those which relate to any other substance not treated of before. For example: as I treat of Acids before Metals, I say nothing under the head of those Acids concerning their power of dissolving metals; that I defer till I come to the subject of Metals: and thus I avoid speaking prematurely of a substance with which I suppose my Reader wholly unacquainted. And this method I was so much the more easily induced to follow, that I know of no Chymical book written on the same Plan. After discoursing of Elements in general, I treat next of such substances as are immediately composed of them, and are, next to them, the most simple: such are all saline substances. This head comprehends mineral Acids, fixed Alkalis, and their several combinations; the volatile sulphureous spirit, sulphur, phosphorus, and the Neutral salts which have an earth or fixed Alkali for their basis: those which have for their basis either a volatile Alkali, or some metallic substance, are referred, according to my general Plan, to the heads under which I treat of those substances. Metallic substances are scarcely more compounded than the saline; which induces me to consider them next. I begin with those which are the most simple, or at least seem to be so; because their principles, being very strongly connected together, are separated with the greatest difficulty: such are the Metals properly so called; namely, Gold, Silver, Copper, Iron, Tin, and Lead. After these come the Semi-metals in order; to wit, Regulus of Antimony, Zinc, Bismuth, and Regulus of Arsenic. Mercury being a doubtful substance, which some Chymists rank with the Metals, and others with the Semi-metals, because it actually possesses certain properties in common with each, I have treated of it in a separate Chapter, which stands between the Metals and Semi-metals. I next proceed to examine the several sorts of Oils, whether Vegetable, which are divided into fat, essential, and empyreumatic; or Animal, and Mineral Oils.