Page:Theophrastus - History of Stones - Hill (1774).djvu/63

 this Change of Colour, is not les eaily and certainly dicoverable from the Colour itelf; than what has influenced the Shape, from the Form. If Lead has furnihed the metalline Particles, the Spar is yellow; if Iron, red; if Tin, black; if Copper, it is either greenih or blueih, according to the Quality of the Mentruum Nature has furnihed for diolving the Particles of that Metal, and bringing them into a State of mixing in the Concretion; for Acids and Alkalis both diolve Copper, but with this Difference of Colour, that the Solution with an Acid is green, and that with an Alkali is blue.

Though this Author was perfectly right, therefore, in his Opinion of thee Subtances partaking of the Nature of the Metals among which they were found; he errs in imagining that they are fuible, and melt with thoe Metals. He may very well, however, be pardoned in this, ince it has been an Error which many later Authors, who had more Opportunities of informing themelves of the Truth than he can reaonably be uppoed to have had, have alo fallen into; nay, and many who imagine they undertand thee Things very well, from the contant Ue of it in fluxing the Ores of Metals, believe the ame of it even yet. This is however an abolutely erroneous Opinion, for Spar is not fuible, but calcines in the Fires ued for melting the Ores of Metals. The Ue it is of, in the fuing them is this: Thoe Ores are frequently clogged and loaded with Sulphurs, which make them very difficult of Fuion; and the Calx of Spar is of the ame Ue in that Cae, that Lime, or any other fixed Alkali would be: That is, it aborbs thoe Sulphurs; and by that means detroying what would impede the Fuion of the Ore, does in ome Sene ait its melting; but no one, who ever aw the Fuion of Ore with its Spar about it, ever yet oberved the leat Particle of that to melt.

The Pyritæ and Molares, as many Kinds of them were originally called, are no more capable of Fuion in the Fire than the Spars. They are Maes of mineral, aline, and XX. Some abolutely affirm, that all Stones will melt in the Fire except Marble, which by burning is reduced to Lime: But this is aying abolutely, and of all, what ought only to be aid in general, and of the greater Number.