EXPERIMENT III.
AN equal Weight of Filings of Copper and Powdered Sal Armoniack, being mixed and put into a Covered Crucible, and kept over a moderate Fire till the Sal Armon. had done Smoaking, as much of the remaing Mass as could be parted was taken out, and looked of a Dark Colour; but being grossly beaten and exposed to the Air, looked like Verdigrease, a substance whose Colour commonly varies, according to the Nature of the Salts concerned in the producti∣on of the Pigment. But a Parcel of the same Mass being grosly beaten, and Hermetically Sealed up from the Air, and left in a South Win∣dow, was not discoloured when that exposed to the Air, had acquired a Virdigrease Colour.