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III. The Metals have been conſidered in another Work: the Stones and Earths of various Kinds, therefore, are to be the Subject of this Treatiſe.
Attainment of that Knowledge; and yet, how imperfect our beſt Diſcoveries by theſe may appear to the induſtrions and ingenious of future Ages, may be gueſſed by the Errors we can diſcover in thoſe of but a few before us.
When Chemiſtry became, ſome Time ago, better underſtood and more practiſed than it had probably ever been before, the Profeſſors of it, finding a certain Number of different Subſtances, into which almoſt al] mixed Bodies were reſolvible, immediately looked upon theſe as fixed and unalterable in themſelves; and as they found them, in a Manner, in all mixed Bodies, they determined that they were the true Principles or Elements of which all Bodies were compounded; fixed their Number, and their Names, viz. That they were five, Spirit, Sulphur, Salt, Water, and Earth. Here then the whole Work ſeemed effected, the Secrets of Nature opened, and the true, fixed, and unalterable Principles of mixed Bodies clearly known.
But what Figure does this boaſted Philoſophy, this Set of Principles now make? when our own Experience, and the Diſcoveries of later Chemiſts give us even the unqueſtionable Teſtimony of our Senſes, that no leſs than three of the five are ſo far from deſerving the Name of Principles or Elements, that they are themſelves mixed Bodies, and reſolvible with proper Care into other diſtinct and different Subſtances. For the ſame Chemiſtry, which has brought Sulphur out of a mixed Body, will alſo ſeparate that Sulphur into Salt, Water, and Earth; and when it has extracted from another, that Salt, they eſteemed ſo true a Principle, will afterwards reduce it alſo into Water and Earth: Spirit alſo, we now find, is no other than Oil attenuated by Salts, and diſſolved in Water. This appears by a plain and eaſy Experiment of Mr. Boyle's, viz. If Spirit of Wine be mixed with ten or twelve times it's Weight of Water, and ſet in a cool Place, the Salts will fly off, the Water will mix itſelf with the Water in the Mixture, and the Oil be left ſwimming at the Top.
Inſtead of the five Principles, therefore, of the Chemiſts before us, farther Diſco-
