And yet before I pass to the next Experiment, I must put you in mind, that the Colours of Metals may in many cases be further alter’d by imploying, either praecipitating Salts, or other convenient Substances to act upon their Solutions.  Of this you may remember, that I have given you several Instances already, to which may be added such as these, That if Quicksilver be dissolv’d in Aqua fortis, and Praecipitated out of the Solution, either with water impregnated with Sea salt, or with the spirit of that Concrete, it falls to the Bottom in the form of a white powder, whereas if it be Praecipitated with an Alcaly, it will afford a Yellowish or tawny powder, and if there be no Praecipitation made, and the Menstruum be drawn off with a convenient fire, the corroded Mercury will remain in the bottom, in the form of a substance that may be made to appear of differing Colours by differing degrees of Heat; As I remember that lately having purposely abstracted Aqua fortis from some Quicksilver that we had dissolv’d in it, so that there remain’d a white Calx, exposing that to several degrees of Fire, and afterwards to a naked one, we obtain’d some new Colours, and at length the greatest part of the Calx lying at the Bottome of the Vial, and being brought partly to a Deep Yellow, and partly to a Red Colour, the rest appear’d elevated to the upper part and neck of the Vial, some in the form of a Reddish, and some of an Ash-Colour Sublimate.  But of the differing Colours which by differing wayes and working of Quick Silver with Fire, and Saline Bodies, may be produc’d in Precipitates, I may elsewhere have occasion to take further notice.  I also told you not long since, that if you corrode Quick-silver with Oyl of Vitriol instead of Aqua-fortis, and abstract the Menstruum, there will remain a White Calx which by the Affusion of Fair Water presently turns into a Lemmon Colour.  And ev’n the Succedaneum to a Menstruum may sometimes serve the turn to change the Colours of a Metal.  The lovely Red which Painters call Vermillion, is made of Mercury, which is of the Colour of Silver, and of Brimstone which is of Kin to that of Gold, Sublim’d up together in a certain proportion, as is vulgarly known to Spagyrists.

EXPERIMENT XLVIII.

The third chief sort of the Adventitious Colours of Metals, is, that which is produc’d by associating them (especially when Calcin’d) with other fusible Bodies, and Principally Venice, and other fine Glass devoid of Colour.

I have formerly given you an Example, whereby it may appear, that a Metal may impart to Glass a Colour much differing from its own, when I told you, how with Silver, I had given Glass a lovely Golden Colour.  And I shall now add, that I have Learn’d from one of the Chief Artificers that sells Painted Glass, that those of his Trade Colour it Yellow with a preparation of the Calx of Silver.  Though having lately