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 XXXIX.

Take the dry'd Buds (or Blossoms) of the Pomegranate Tree, (which are com∣monly call'd in the Shops (Balaustiums) pull off the Reddish Leaves, and by a gentle Ebullition of them in fair Water, or by a competent Infusion of them in like Water well heated, extract a faint Reddish Tin∣cture, which if the Liquor be turbid, you may Clarifie it by Filtrating it. Into this, if you pour a little good Spirit of Urine, or some other Spirit abounding in the like sort of Volatile Salts, the Mixture will

presently turn of a dark Greenish Colour, but if instead of the fore-mention'd Li∣quor, you drop into the simple Infusion a little rectify'd Spirit of Sea-Salt, the Pale and almost Colourless Liquor will imme∣diately not only grow more Transparent, but acquire a high Redness, like that of Rich Claret Wine, which so suddenly ac∣quir'd Colour, may as quickly be Destroy'd and turn'd into a dirty Blewish Green, by the affusion of a competent quantity of the above-mention'd Spirit of Urine.

Annotation.

This Experiment may bring some Light to, and receive some from a couple of other Experiments, that I remember I have met with in the Ingenious Gassendus's Animad∣versions upon Epicurus's Philosophy, whilst I was turning over the Leaves of those Learned Commentaries; (my Eyes being too weak to let me read such Voluminous Books quite thorough) And I the less scruple (notwithstanding my contrary Cu∣stom in this Treatise) to set down these Experiments of another, because I shall a little improve the latter of them, and be∣cause by comparing there with that which I have last recited, we may be assisted to Con∣jecture

upon what account it is, that Oyl of Vitriol heightens the Tincture of Red-rose Leaves, since Spirit of Salt, which is a highly Acid Menstruum, but otherwise differing enough from Oyl of Vitriol, does the same thing. Our Authors Experiments then, as we made them, are these; We took about a Glass-full of luke-warm Wa∣ter, and in it immerg'd a quantity of the Leaves of Senna, and presently upon the Immersion there did not appear any Red∣ness in the Water, but dropping into it a little Oyl of Tartar, the Liquor soon dis∣cover'd a Redness to the watchfull Eye, whereas by a little of that Acid Liquor of Vitriol, which is like the former, undeser∣vedly called Oyl, such a Colour would not be extracted from the infused Senna. On the other side we took some Red-rose Leaves dry'd, and having shaken them into a Glass of fair Water, they imparted to it no Redness, but upon the affusion of a little Oyl of Vitriol the Water was imme∣diately turn'd Red, which it would not have been, if instead of Oyl of Vitriol, we had imployed Oyl of Tartar to produce that Colour: That these were Gassendus his Experiments, I partly remember, and was assur'd by a Friend, who lately Transcribed them out of Gassendus his Book, which I

therefore add, because I have not now that Book at hand. And the design of Gassen∣dus in these Experiments our Friend affirms to be, to prove, that of things not Red a Redness may be made only by Mixture, and the Varied position of parts, wherein the Doctrine of that Subtil Philosopher doth not a little Authorize, what we have formerly delivered concerning the Emer∣gency and Change of Colours. But the instances, that we have out of him set down, seem not to be the most Eminent, that may be produced of this truth: For our next Experiment will shew the production of several Colours out of Liquors, which have not any of them any such Colour, nor indeed any discernable one at all; and whereas though our Author tells us, that there was no Redness either in the Water, or the Leaves of Senna, or the Oyl of Tar∣tar; And though it be true, that the Pre∣dominant Colour of the Leaves of Senna be another than Red, yet we have try'd, that by steeping that Plant a Night even in Cold water, it would afford a very deep Yellow or Reddish Tincture without the help of the Oyl of Tartar, which seems to do little more than assist the Water to ex∣tract more nimbly a plenty of that Red Tincture, wherewith the Leaves of Senna

do of themselves abound, and having taken off the Tincture of Senna, made only with fair Water, before it grew to be Reddish, and Decanted it from the Leaves, we could not perceive, that by dropping some Oyl of Tartar into it, that Colour was considera∣ble, though it were a little heightned into a Redness, which might have been expected, if the particles of the Oyl did eminently Co-operate, otherwise than we have ex∣pressed, to the production of this Red∣ness.

And as for the Experiment with Red-rose Leaves, the same thing may be alle∣ged, for we found that such Leaves by bare Infusion for a Night and Day in fair Water, did afford us a Tincture bordering at least upon Redness, and that Colour being conspicuous in the Leaves themselves, would not by some seem so much to be produc'd as to be extracted by the affusion of Oyl of Vitriol. And the Experiment try'd with the dry'd Leaves of Damask-roses succeeded but imperfectly, but that is indeed observable to our Authors purpose, that Oyl of Tartar will not perform in this Experiment what Oyl of Vitriol doth; but because this last named Liquor is not so easily to be had, give me leave to Adver∣tise you, that the Experiment will succeed,

if Instead of it you imploy Aqua-fortis. And though some Trials of our own for∣merly made, and others easily deducible from what we have already deliver'd, about the different. Families and Operations of Salt, might enable us to present you an Experiment upon Red-rose Leaves, more accommodated to our Authors purpose, than that which he hath given us; yet our Reverence to so Candid a Philosopher, in∣vites us rather to improve his Experiment, than substitute another in its place. Take therefore of the Tincture of Red-rose Leaves, (for with Damask-rose Leaves the Experiment succeedeth not well) made as before hath been taught with a little Oyl of Vitriol, and a good quantity of fair Water, pour off this Liquor into a clear Vial, half fill'd with Limpid water, till the Water held against the Light have ac∣quir▪d a competent Redness, without lo∣sing its Transparency, into this Tincture drop leisurely a little good Spirit of Urine, and shaking the Vial, which you must still hold against the Light, you shall see the Red Liquor immediately turn'd into a fine Greenish Blew, which Colour was not to be found in any of the Bodies, upon whose Mixture it emerg'd, and this Change is the more observable, because in many Bo∣dies

the Degenerating of Blew into Red is usual enough, but the turning of Red into Blew is very unfrequent. If at every drop of Spirit of Urine you shake the Vial containing the Red Tincture, you may de∣lightfully observe a pretty variety of Co∣lours in the passage of that Tincture from a Red to a Blew, and sometimes we have this way hit upon such a Liquor, as being look't upon against and from the Light, did seem faintly to emulate the above-men∣tion'd Tincture of Lignum Nephriticum. And if you make the Tincture of Red-roses very high, and without Diluting it with fair Water, pour on the Spirit of Urine, you may have a Blew so deep, as to make the Liquor Opacous, but being dropt upon White Paper the Colour will soon disclose it self. Also having made the Red, and consequently the Blew Tin∣cture very Transparent, and suffer'd it to rest in a small open Vial for a Day or two, we found according to our Conjecture, that not only the Blew but the Red Colour also was Vanish'd; the clear Liquor being of a bright Amber Colour, at the bottom of which subsided a Light, but Copious fe∣culency of almost the same Colour, which seems to be nothing but the Tincted parts of the Rose Leaves drawn out by the Acid

Spirits of the Oyl of Vitriol, and Precipi∣tated by the Volatile Salt of the Spirit of Urine, which makes it the more probable, that the Redness drawn by the Oyl of Vi∣triol, was at least as well an extraction of the Tinging parts of the Roses, as a pro∣duction of Redness; and lastly, if you be destitute of Spirit of Urine, you may change the Colour of the Tincture of Roses with many other Sulphureous Salts, as a strong Solution of Pot-ashes, Oyl of Tartar, &c. which yet are seldome so free from Fecu∣lency, as the Spirituous parts of Urine be∣comes by repeated Distillation.

Annotation.

On this occasion, I call to mind, that I found, a way of producing, though not the same kind of Blew, as I have been mentioning, yet a Colour near of Kin to it, namely, a fair Purple, by imploying a Liquor not made Red by Art, instead of the Tincture of Red-roses, made with an Acid Spirit; And my way was only to take Log-wood, (a Wood very well known to Dyers) having by Infusion the Powder of it a while in fair Water made that Li∣quor Red, I dropt into it a Tantillum of an Urinous Spirit, as that of Sal-Armoniack,

(and I have done the same thing with an Alcali) by which the Colour was in a moment turn'd into a Rich, and lovely Purple. But care must be had, that you let not fall into a Spoonfull above two or three Drops, left the Colour become so deep, as to make the Liquor too Opacous. And (to answer the other part of Gassendus his Experiment) if instead of fair Water, I infus'd the Log-wood in Water made somewhat sowr by the Acid Spirit of Salt, I should obtain neither a Purple Liquor, nor a Red, but only a Yellow one.