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different kinds, particularly of the latter ; which they ad-mitted as many varieties of as there are metals ; and which,in gold, they held to be pure, red, fixt and incombustible,but of different qualities in the other metals. In thesepoints there is no perfect uniformity among the differentalchemical philosophers, which indeed could not be ex-pected in hypotheses on so abstruse a subject, where ex-perience had afforded so little light : some have added asaline, some an earthy, and others an arsenical principle.

They supposed that the pure mercurial, sulphureous, orother principles of which they imagined gold to be com-posed, were contained, separately, in certain other bodies.These principles therefore they endeavoured to collect,and to concoct and incorporate by long digestions. In themany volumes written professedly to teach the process atfull length, the subjects, from which the golden feeds areto be obtained, are wrapt in impenetrable obscurity : thusmuch is plain, that the supposed adepts in this mysteriousscience do not all make choice of the same subjects, orwork upon them in the same manner, their practice beingprobably adapted to their particular hypotheses.

By thus conjoining the principles of gold, if theycould be so procured and conjoined, it might be ex-pected that gold would be produced. But the alchemistspretend to a product of a higher order, called the elixir,the medicine for metals, the tincture, the philosophersstone ; which, by being projected on a large quantity ofany of the inferiour metals in fusion, should change theminto fine gold ; which, being laid on a plate of silver,copper, or iron, and moderately heated, should sinkinto the metal, and change into gold all the parts itwas applied on ; which, on being properly treated withpure gold, should change the gold into a substance ofthe same nature and virtue with itself, so as thus to be

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