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 ...

EXPERIMENT III.

If pieces of White Harts-horn be with a competent degree of fire distill'd in a Glass∣retort, they will, after the avolation of the Flegm, Spirit, Volatile Salt, and the looser and lighter parts of the Oleagenous sub∣stance, remain behind of a Cole-black colour. And even Ivory it self being skilfully Burnt (how I am wont to do it, I have else∣where set down) affords Painters one of the best and deepest Blacks they have, and yet in the Instance of distill'd Harts-horn, the operation being made in Glass-vessels carefully clos'd, it appears there is no Extra∣neous Black substance that Insinuates it self into White Harts-horn, and thereby makes it turn Black; but that the Whiteness is de∣stroy'd, and the Blackness generated, only by a Change of Texture, made in the burnt Body, by the Recess of some parts and the Transposition of others. And though I re∣member not that in many Distillations of Harts-horn I ever found the Cap. Mort. to pass from Black to a true Whiteness, whilst it continu'd in Clos'd vessels, yet having ta∣ken out the Cole-black fragments, and Cal∣cin'd them in Open vessels, I could in few hours quite destroy that Blackness, & with∣out

sensibly changing their Bulk or Figure, reduce them to great Whiteness. So much do these two Colours depend upon the Dis∣position of the little parts, that the Bodies wherein they are to be met with do consist of. And we find, that if Whitewine Tar∣tar, or even the white Crystalls of such Tartar be burnt without being truly Cal∣cin'd, the Cap. Mortuum (as the Chy∣mists call the more Fixt part) will be Black. But if you further continue the Calcination till you have perfectly Incinerated the Tar∣tar, & kept it long enough in a Strong fire, the remaining Calx will be White. And so we see that not only other Vegetable sub∣stances, but even White woods, as the Hazel, will yield a Black Charcoal, and afterwards Whitish ashes; And so Animal substances naturally White, as Bones and Eggshels, will grow Black upon the being Burnt, and White again when they are per∣fectly Calcin'd.