Experiments and considerations touching colours first occasionally written, among some other essays to a friend, and now suffer'd to come abroad as the beginning of an experimental history of colours / by the Honourable Robert Boyle ...

Annotation III.

And yet before I pass to the next Ex∣periment, I must put you in mind, that the Colours of Metals may in many cases be further alter'd by imploying, either praeci∣pitating Salts, or other convenient Substan∣ces 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 Praecipita∣ted out of the Solution, either with water impregnated with Sea salt, or with the spi∣rit 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 ab∣stracted Aqua fortis from some Quicksil∣ver 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 part∣ly to a Red Colour, the rest appear'd ele∣vated to the upper part and neck of the Vi∣al, 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 Precipi∣tates, 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 re∣main a White Calx which by the Affusion of Fair Water presently turns into a Lem∣mon Colour. And ev'n the Succedaneum to a Menstruum may sometimes serve the turn to change the Colours of a Metal. The love∣ly

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.