Page:Theophrastus - History of Stones - Hill (1774).djvu/23

 Attainment of that Knowledge; and yet, how imperfect our bet Dicoveries by thee may appear to the indutrions and ingenious of future Ages, may be gueed by the Errors we can dicover in thoe of but a few before us.

When Chemitry became, ome Time ago, better undertood and more practied than it had probably ever been before, the Profeors of it, finding a certain Number of different Subtances, into which almot al] mixed Bodies were reolvible, immediately looked upon thee as fixed and unalterable in themelves; 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 eemed effected, the Secrets of Nature opened, and the true, fixed, and unalterable Principles of mixed Bodies clearly known.

But what Figure does this boated Philoophy, this Set of Principles now make? when our own Experience, and the Dicoveries of later Chemits give us even the unquetionable Tetimony of our Senes, that no les than three of the five are o far from deerving the Name of Principles or Elements, that they are themelves mixed Bodies, and reolvible with proper Care into other ditinct and different Subtances. For the ame Chemitry, which has brought Sulphur out of a mixed Body, will alo eparate that Sulphur into Salt, Water, and Earth; and when it has extracted from another, that Salt, they eteemed o true a Principle, will afterwards reduce it alo into Water and Earth: Spirit alo, we now find, is no other than Oil attenuated by Salts, and diolved in Water. This appears by a plain and eay Experiment of Mr. Boyle's, viz. If Spirit of Wine be mixed with ten or twelve times it's Weight of Water, and et in a cool Place, the Salts will fly off, the Water will mix itelf with the Water in the Mixture, and the Oil be left wimming at the Top.

Intead of the five Principles, therefore, of the Chemits before us, farther III. The Metals have been conidered in another Work: the Stones and Earths of various Kinds, therefore, are to be the Subject of this Treatie.