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.
By examining these substances we obtain ideas of all the principles which enter into the composition of Vegetable and Animal bodies; that is, of those substances that are capable of fermentation: this enables me to treat of fermentation in general; of its three different degrees or kinds, the spirituous, acetous, and putrid; and of the products of those fermentations, ardent spirits, acids analogous to those of vegetables and animals, and volatile alkalis.
The order in which I treat of all those substances being different from that in which they are obtained from compound bodies, I give, in a distinct Chapter, a general idea of Chymical Decomposition, with a view to shew the order in which they are separated, from the several bodies in the composition whereof they are found. This brings them a second time under review, and gives me an opportunity of distinguishing those which exist naturally in compound bodies, from those which are only the result of a new combination of some of their principles produced by the fire.
The succeeding Chapter explains the late Mr Geoffroy's Table of Affinities; which I take to be of great use at the end of an Elementary tract like this, as it collects into one point of view the most essential and fundamental doctrines which are dispersed through the work.
I conclude with an account of the Construction of such Vessels and Furnaces as are usually employed in Chymistry.
In this Part I say nothing of any manual operations, or the several ways of performing Chymical processes; reserving these particulars for my Treatise of Practical Chymistry, to which this must be considered as an Introduction.