Thing; the ſame univerſal mineral Acid, exeiſtent every where in the Earth, and ſometimes perceivable by the Senſes, in the ſuffocating Damps of Mines, being the certain Baſis of both; as alſo of a third, that of Alum: And though the different Matter it meets with in Alum, Vitriol, and Sulphur, gives it a different Appearance in the Concrete, yet when freed from that Matter by Chemiſtry, and rendered as pure as that Art will make it, it appears the ſame Thing, whether drawn from one or the other of theſe Subſtances.
That Oil of Vitriol, therefore, and Oil of Sulphur, ſhould produce a Solution of Copper of the ſame Colour, is no other than what muſt naturally be expected: But that Agua fortis, which is a compound Menſtruum, and made, though partly from Vitriol, which affords a blue Solution, yet partly alſo from Nitre, which we have ſeen before affords a fine green one, ſhould give a ſimply blue Solution, as it evidently does, without the leaſt Admixture of Green, may ſeem, at firſt View, ſomething ſtrange. But here I muſt obſerve, that Spirit of Nitre is the Menſtruum I hinted at in the Beginning of this Letter, as capable of affording different Colours, from different Quantities of the Metal diſſolved in it. And nothing, indeed, is more certain, than that the greeneſt Solution of Copper in Spirit of Nitre, may be turned into a pale Blue, only by adding more and more Filings of the ſame Metal, up to the proper Quantity for the Change.
