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 II.

Make a strong Infusion of broken Galls in Fair Water, and having Filtred it into a clean Vial, add more of the same liquor to it, till you have made it somewhat Transpa∣rent, and sufficiently diluted the Colour, for the credit of the Experiment, lest o∣therwise the Darkness of the liquor might make it be objected, that 'twas already al∣most Ink; Into this Infusion snake a conve∣nient quantity of a Cleer, but very strong Solution of Vitriol, and you shall immedi∣ately see the mixture turn Black almost like Ink, and such a way of producing Black∣ness is vulgar enough; but if presently after you doe upon this mixture drop a small quantity of good oyl of Vitriol, and, by shaking the Vial disperse it nimbly through the two other liquors, you shall (if you perform your part well, and have employ'd oyl of Vitriol Cleer and Strong enough) see the Darkness of the liquor presently begin

to be discuss'd, and grow pretty Cleer and Transparent, losing its Inky Blackness, which you may again restore to it by the affusion of a small quantity of a very strong Solution of Salt of Tartar. And though neither of these Atramentous liquors will seem other than very Pale Ink, if you write with a clean Pen dipt in them, yet that is common to them with some sorts of Ink that prove ve∣ry good when Dry, as I have also found, that when I made these carefully, what I wrote with either of them, especially with the For∣mer, would when throughly Dry grow Black enough not to appear bad Ink. This Experiment of taking away and restoring Blackness from and to the liquors, we have likewise tryed in Common Ink; but there it succeeds not so well, and but very slowly, by reason that the Gum wont to be em∣ployed in the making it, does by its Tenacity oppose the operations of the above men∣tion'd Saline liquors. But to consider Gum no more, what some kind of Praecipitation may have to do in the producing and de∣stroying of Inks without it, I have elsewhere given you some occasion and assistance to enquire; But I must not now stay to do so my self, only I shall take notice to you, that though it be taken for granted that bodies will not be Praecipitated by Alcaliz at Salts,

that have not first been dissolved in some Acid Menstruums, yet I have found upon tryals, which my conjectures lead me to make on purpose, That divers Vegetables barely infus'd, or, but slightly decocted in common water, would, upon the affusion of a Strong and Cleer Lixivium of Potashes, and much more of some other Praecipitating liquors that I sometimes employ, afford good store of a Crudled matter, such as I have had in the Praecipitations of Vegetable substances, by the intervention of Acid things, and that this matter was easily separable from the rest of the liquor, being left be∣hind by it in the Filtre; and in making the first Ink mention'd in this Experiment, I found that I could by Filtration separate pretty store of a very Black pulverable sub∣stance, that remain'd in the Filtre, and when the Ink was made Cleer again by the Oyl of Vitriol, the affusion of dissolv'd Sal Tartari seem'd but to Praecipitate, and thereby to Unite and render Conspicuous the particles of the Black mixture that had before been dispers'd into very Minute and singly Invi∣sible particles by the Incisive and resolving power of the highly Corrosive Oyl of Vi∣triol.