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 X.

We have sometimes found in the Shops of our Druggists, a certain Wood, which is there call'd Lignum Nephriticum, because the Inhabitants of the Country where it grows, are wont to use the Infusion of it made in fair Water against the Stone of the Kidneys, and indeed an Eminent Physician of our Acquaintance, who has very Particularly enquir'd into that Disease, assures me, that he has found such an Infu∣sion one of the most effectual Remedyes, which he has ever tried against that formi∣dable Disease. The ancientest Account I have met: with of this Simple, is given us by the Experienc'd Monardes in these Words.

Nobis, says he, Nova Hispania mittit quod∣dam ligni genus crassum & enode, cujus usus jam diu receptus fuit in his Regionibus ad Renum vitia & Urinae difficul∣tates ac arenulas pellendas. Fit autem hac ratione, Lignum as∣sulatim & minutim concisum in limpidissima aqua fontana maceratur, inque ea¦relinquitur, donec aqua à bibentibus absumpta fit, dimidia hora post injectum lignum aqua Coeruleum colorem contrahit, quisensim inten∣ditur pro temporis diuturnitate, tametsi lig∣num candidum sit. This Wood, Pyrophilus, may afford us an Experiment, which be∣sides the singularity of it, may give no small assistance to an attentive Considerer to∣wards the detection of the Nature of Co∣lours. The Experiment as we made it is this. Take Lignum Nephriticum, and with a Knife cut it into thin Slices, put about a handfull of these Slices into two three or four pound of the purest Spring-water, let them infuse there a night, but if you be in hast, a much shorter time may suffice; de∣cant this Impregnated Water into a clear Glass Vial, and if you hold it directly be∣tween the Light and your Eye, you shall see it wholly Tincted (excepting the very top of the Liquor, wherein you will some times discern a Sky-colour'd Circle) with

an almost Golden Colour, unless your In∣fusion have been made too Strong of the Wood, for in that case it will against the Light appear somewhat Dark and Reddish, and requires to be diluted by the addition of a convenient quantity of fair Water. But if you hold this Vial from the Light, so that your Eye be plac'd betwixt the Win∣dow and the Vial, the Liquor will appear of a deep and lovely Coeruleous Colour, of which also the drops, if any be lying on the out-side of the Glass, will seem to be very perfectly; And thus far we have try'd the Experiment, and found it to succeed even by the Light of Candles of the larger size. If you so hold the Vial over against your Eyes, that it may have a Window on one side of it, and a Dark part of the Room both before it and on the other side, you shall see the Liquor partly of a Blewish and partly of a Golden Colour. If turning your back to the Window, you powr out some of the Liquor towards the Light and towards your Eyes, it will seem at the comming out of the Glass to be perfectly Coeruleous, but when it is sallen down a little way, the drops may seem Partico∣lour'd, according as the Beams of Light do more or less fully Penetrate and Illu∣strate them. If you take a Bason about

half full of Water, and having plac'd it so in the Sun-beams Shining into a Room, that one part of the Water may be freely Illu∣strated by the Beams of Light, and the other part of it Darkned by the shadow of the Brim of the Bason, if then I say you drop of our Tincture, made somewhat strong, both into the Shaded and Illuminated parts of the Water, you may by looking upon it from several places, and by a little Agita∣tion of the water, observe divers pleasing Phoenomena which were tedious to parti∣cularize. If you powr a little of this Tin∣cture upon a sheet of White Paper, so as the Liquor may remain of some depth upon it, you may perceive the Neighbouring drops to be partly of one Colour, and partly of the other, according to the position of your Eye in reference to the Light when it looks upon them, but if you powr off all the Li∣quor, the Paper will seem Dy'd of an almost Yellow Colour. And if a sheet of Paper with some of this Liquor in it be plac'd in a window where the Sunbeams may shine freely on it, then if you turn your back to the Sun and take a Pen or some such slender Body, and hold it over-thwart betwixt the Sun and the Liquor, you may perceive that the Shadow projected by the Pen up∣on the Liquor, will not all of it be a vulgar

and Dark, but in part a curiously Colour'd shadow, that edge of it, which is next the Body that makes it, being almost of a lively Golden Colour, and the remoter verge of a Coeruleous one.

These and other Phoenomena, which I have observ'd in this delightfull Experi∣ment, divers of my friends have look'd up∣on not without some wonder, and I re∣member an excellent Oculist finding by accident in a friends Chamber a fine Vial full of this Liquor, which I had given that friend, and having never heard any thing of the Experiment, nor having any Body near him that could tell him what this strange Liquor might be, was a great while apprehensive, as he presently after told me, that some strange new distemper was in∣vading his Eyes. And I confess that the unusualness of the Phoenomena made me very sollicitous to find out the Cause of this Experiment, and though I am far from pretending to have found it, yet my en∣quiries have, I suppose, enabled me to give such hints, as may lead your greater sa∣gacity to the discovery of the Cause of this wonder. And first finding that this Tincture, if it were too copious in the water, Kept the Colours from being so lively, and their Change from being so discernable, and

finding also that the Impregnating Virtue of this Wood did by its being frequently Infus'd in New Water by degrees Decay, I Conjectur'd that the Tincture afforded by the Wood must proceed from some Subtiler parts of it drawn forth by the Water, which swimming too and fro in it did so Modifie the Light, as to exhibit such and such Colours; and because these Subtile parts were so easily Soluble even in Cold water, I concluded that they must abound with Salts, and perhaps contain much of the Essential Salt, as the Chymists call it, of the Wood. And to try whether these Subtile parts were Volatile enough to be Distill'd, without the Dissolution of their Texture, I carefully Distill'd some of the Tincted Liquor in very low Vessels, and the gentle heat of a Lamp Furnace; but found all that came over to be as Limpid and Colourless as Rock-water, and the Liquor remaining in the Vessel to be so deeply Coeruleous, that it requir'd to be oppos'd to a very strong Light to appear of any other Colour. I took likewise a Vial with Spirit of Wine, and a little Salt of Harts-horn, and found that there was a certain proportion to be met with betwixt the Liquor and the Salt, which made the Mixture fit to exhibit some little Variety

of Colours not Observable in ordinary Liquors, as it was variously directed in reference to the Light and the Eye, but this Change of Colour was very far short from that which we had admir'd in our Tincture. But however, I suspected that the Tinging Particles did abound with such Salts, whose Texture, and the Colour springing from it, would probably be al∣ter'd by peircing Acid Salts, which would in likelihood either make some Dissipation of their Parts, or Associate themselves to the like Bodies, and either way alter the Colour exhibited by them; whereupon Pouring into a small Vial full of Impreg∣nated Water, a very little Spirit of Vine∣gar, I found that according to my Expe∣ctation, the Coeruleous Colour immedi∣ately vanish'd, but was deceiv'd in the Expectation I had, that the Golden Colour would do so too; for, which way soever I turned the Vial, either to or from the Light, I found the Liquor to appear al∣ways of a Yellowish Colour and no other: Upon this I imagin'd that the Acid Salts of the Vinegar having been able to deprive the Liquor of its Coeruleous Colour, a Sulphureous Salt being of a contrary Na∣ture, would be able to Mortifie the Saline Particles of Vinegar, and Destroy their

Effects; And accordingly having plac'd my Self betwixt the Window, and the Vial, and into the same Liquor dropt a few drops of Oyl of Tartar per Deliquium, (as Chymists call it) I observ'd with plea∣sure, that immediately upon the Diffusion of this Liquor, the Impregnated Water was restor'd to its former Coeruleous Co∣lour; And this Liquor of Tartar being very Ponderous, and falling at first to the Bottom of the Vial, it was easie to observe that for a little while the Lower part of the Liquor appear'd deeply Coeruleous, whilst all the Upper part retain'd its former Yel∣lowness, which it immediately lost as soon as either Agitation or Time had made a competent Diffusion of the Liquor of Tar∣tar through the Body of the former Tin∣cture; and this restor'd Liquor did, as it was Look'd upon against or from the Light, exhibit the same Phaenomena as the Tincted Water did, before either of the Adven∣titious Liquors was pour'd into it.

Having made, Pyrophilus, divers Tryals upon this Nephritick Wood, we found mention made of it by the Industrious Je∣suit Kircherus, who having received a Cup Turned of it from the Mexican Procurator of his Society, has probably receiv'd also from him the Information he gives us con∣cerning

that Exotick Plant, and therefore partly for that Reason, and partly because what he Writes concerning it, does not perfectly agree with what we have deli∣ver'd, we shall not Scruple to acquaint you in his own Words, with as much of what he writes concerning our Wood, as is requisite to our present purpose. Hoc loco (says he) neutiquam omittendum duximus quoddam ligni candidi Mexicani genus, quod Indigenae Coalle & Tlapazatli vocant, quod etsi ex∣perientia hucusque non nisi Coe∣ruleoaquam colore tingere docuerit, nos tamen continua experientia invenimus id aquam in omne Colorum genus transformare, quod merito cuipiam Paradoxum videri posset; Ligni frutex grandis, ut aiunt, non rarò in molem arboris excrescit, truncus illius est crassus, enodis, instar piri arboris, folia ciceris foliis, aut rutae haud absimilia, flores exigui, oblongi, lutei & spicatim digesti; est frigida & humida planta, licet parum recedat à medio tempera∣mento. Hujus itaque descriptae arboris lignum in poculum efformatum, aquam eidem infusam primu in aquam intense Coeruleam, colore floris Baglossae, tingit, & quo diutius in eo steterit, tanto intensiorem colorem acquirit. Hanc igitur aquam si Vitreu Sphaerae infuderis, luci∣que exposueris, ne ullum quidem Coerulei co∣loris

vestigium apparebit, sed instar aquae purae putae fontanae limpidam claramque aspi∣cientibus se praebebit. Porro si hanc phialam vitream versus locum magis umbrosum di∣rexeris, totus humor gratissimum virorem re∣feret; si adhuc umbrosioribus locis, subru∣brum, & sic pro rerum objectarum conditione, mirum dictu, colorem mutabit; in tenebris verò vel in vase opaco posita, Coeruleum colo∣rem suum resumet.

In this passage we may take notice of the following Particulars. And first, he calls it a White Mexican Wood, whereas (not to mention that Mornardes informs us that it is brought out of Nova Hispania) the Wood that we have met with in several places, and employ'd as Lignum Nephri∣ticum, was not White, but for the most part of a much Darker Colour, not unlike that of the Sadder Colour'd Wood of Juniper. 'Tis true, that Monardes himself also says, that the Wood is White; and it is affirm'd, that the Wood which is of a Sadder Colour is Adulterated by being Imbu'd with the Tincture of a Vegetable, in whose Decoction it is steep'd. But ha∣ving purposely enquir'd of the Eminentest of our English Druggists, he peremptorily deny'd it. And indeed, having consider'd some of the fairest Round pieces of this

Wood that I could meet with in these Parts, I had Opportunity to take notice that in one or two of them it was the Ex∣ternal part of the Wood that was White, and the more Inward part that was of the other Colour, the contrary of which would probably have appear'd, if the Wood had been Adulterated after the afore-mention'd manner. And I have at present by me a piece of such Wood, which for about an Inch next the Bark is White, and then as it were abruptly passes to the above-mention'd Colour, and yet this Wood by the Tincture, it afforded us in Water, appears to have its Colour'd part Genuine enough; for as for the White part, it appears upon tryal of both at once, much less enrich'd with the tingent Pro∣perty.

Next, whereas our Author tells us, that the Infusion of this Wood expos'd in a Vial to the Light, looks like Spring-water, in which he afterwards adds, that there is no Tincture to be seen in it, our Obser∣vation and his agree not, for the Liquor, which opposed to the Darker part of a Room exhibits a Sky-colour, did constant∣ly, when held against the Light, appear Yellowish or Reddish, according as its Tincture was more Dilute or Deep; and

then, whereas it has been already said, that the Coeruleous Colour was by Acid Salts a bolished, this Yellowish one surviv'd without any considerable Alteration, so that unless our Author's Words be taken in a very Limited Sense, we must conclude, that either his Memory mis-inform'd him, or that his White Nephritick Wood, and the Sadder Colour'd one which we em∣ploy'd, were not altogether of the same Nature: What he mentions of the Cup made of Lignum Nephriticum, we have not had Opportunity to try, not having been able to procure pieces of that Wood great enough, and otherwise fit to be turned into Cups; but as for what he says in the Title of his Experiment, that this Wood tinges the Water with all sorts of Co∣lours, that is much more than any of those pieces of Nephritick Wood that we have hitherto employ'd, was able to make good; The change of Colours discernable in a Vial full of VVater, Impregnated by any of them, as it is directed towards a place more Lightsome or Obscure, being far from affording a Variety answerable to so pro∣mising a Title. And as for what he tells us, that in the Dark the Infusion of our VVood will resume a Coeruleous Colour, I wish he had Inform'd us how he Try'd it.

But this brings into my mind, that ha∣ving sometimes for Curiosity sake, brought a round Vial with a long Neck fill'd with the Tincture of Lignum Nephriticum into the Darken'd Room already often menti∣on'd, and holding it sometimes in, some∣times near the Sun-beams that enter'd at the hole, and sometimes partly in them, and partly out of them, the Glass being held in several postures, and look'd upon from several Neighbouring parts of the Room, disclos'd a much greater Variety of Colours than in ordinary inlightn'd Rooms it is wont to do; exhibiting, besides the usual Colours, a Red in some parts, and a Green in others, besides Intermediate Colours produc'd by the differing Degrees, and odd mixtures of Light and Shade.

By all this You may see, Pyrophilus, the reasonableness of what we elsewhere had occasion to mention, when we have divers times told you, that it is usefull to have New Experiments try'd over again, though they were, at first, made by Knowing and Candid Men, such Reiterations of Expe∣riments commonly exhibiting some New Phoenomena, detecting some Mistake or hinting some Truth, in reference to them, that was not formerly taken notice of. And some of our friends have been pleas'd to

think, that we have made no unusefull additi∣on to this Experiment, by shewing a way, how in a moment our Liquor may be de∣priv'd of its Blewness, and restor'd to it a∣gain by the affusion of a very few drops of Licuors, which have neither of them any Colour at all of their own. And that which deserves some particular wonder, is, that the Coeruleous Tincture of our Wood is subject by the former Method to be De∣stroy'd or Restor'd, the Yellowish or Red∣dish Tincture continuing what it was. And that you may see, that Salts are of a consi∣derable use in the striking of Colours, let me add to the many Experiments which may be afforded us to this purpose by the Dyers Trade, this Observation; That as far as we have hitherto try'd, those Liquors in general that are strong of Acid Salts have the Power of Destroying the Blew∣ness of the Infusion of our Wood, and those Liquors indiscriminatly that abound with Sulphureous Salts, (under which I compre∣hend the Urinous and Volatile Salts of Animal Substances, and the Alcalisate or fixed Salts that are made by Incineration) have the vertue of Restoring it.

A Corollary of the Tenth Experiment.

That this Experiment, Pyrophilus, may be as well Usefull as Delightfull to You, I must mind You, Pyrophilus, that in the newly mention'd Observation, I have hin∣ted to You a New and Easie way of Dis∣covering in many Liquors (for I dare not say in all) whether it be an Acid or Sul∣phureous Salt, that is Predominant; and that such a Discovery is oftentimes of great Difficulty, and may frequently be of great Use, he that is not a Stranger to the various Properties and Effects of Salts, and of how great moment it is to be able to distinguish their Tribes, may readily conceive. But to proceed to the way of trying other Liquors by an Infusion of our Wood, take it briefly thus. Suppose I have a mind to try whe∣ther I conjecture aright, when I imagine that Allom, though it be plainly a Mixt Bo∣dy, does abound rather with Acid than Sulphureous Salt. To satisfie my self here∣in, I turn my back to the Light, and hold∣ing a small Vial full of the Tincture of Lignum Nephriticum, which look'd upon in that Position, appears Coeruleous, I drop into it a little of a strong Solution of Allom made in Fair Water, and finding upon the

Affusion and shaking of this New liquor, that the Blewness formerly conspicuous in our Tincture does presently vanish, I am thereby incited to suppose, that the Salt Praedominant in Allom belongs to the Fa∣mily of Sour Salts; but if on the other side I have a mind to examine whether or no I rightly conceive that Salt of Urine, or of Harts-horn is rather of a Saline Sulphu∣reous (if I may so speak) than of an Acid Nature, I drop a little of the Saline Spirit of either into the Nephritick Tincture, and finding that the Coeruleous Colour is rather thereby Deepned than Destroy'd, I collect that the Salts, which constitute these Spi∣rits, are rather Sulphureous than Acid. And to satisfie my self yet farther in this particu∣lar, I take a small Vial of fresh Tincture, and placing both it and my self in reference to the Light as formerly, I drop into the Infusion just as much Distill'd Vinegar, or other Acid liquor as will serve to Deprive it of its Blewness (which a few drops, if the Sour Liquor be strong, and the Vial small will suffice to do) then without changing my Posture, I drop and shake into the same Vial a small proportion of Spirit of Harts-horn or Urine, and finding that upon this affusion, the Tincture immediately recovers its Coeruleous Colour, I am thereby con∣firm'd

in my former Opinion, of the Sul∣phureous Nature of these Salts. And so, whereas it is much doubted by some Mo∣dern Chymists to what sort of Salt, that which is Praedominant in Quick-lime be∣longs, we have been perswaded to referr it rather to Lixiviate than Acid Salts, by having observ'd, that though an Evaporated Infusion of it will scarce yield such a Salt, as Ashes and other Alcalizate Bodyes are wont to do, yet if we deprive our Nephri∣tick Tincture of its Blewness by just so much Distill'd Vinegar as is requisite to make that Colour Vanish, the Lixivium of Quick-lime will immediately upon its Affusion recall the Banished Colour; but not so Powerfully as either of the Sulphureous Li∣quors formerly mention'd. And therefore I allow my self to guess at the Strength of the Liquors examin'd by this Experiment, by the Quantity of them which is sufficient to Destroy or Restore the Coeruleous Co∣lour of our Tincture. But whether con∣cerning Liquors, wherein neither Acid nor Alcalisate Salts are Eminently Praedomi∣nant, our Tincture will enable us to con∣jecture any thing more than that such Salts are not Praedominant in them, I take not up∣on me to determine here, but leave to fur∣ther Tryal; For I find not that Spirit of

Wine, Spirit of Tartar freed from Acidity, or Chymical Oyl of Turpentine, (although Liquors which must be conceiv'd very Sa∣line, if Chymists have, which is here no place to Dispute, rightly ascrib'd tasts to the Saline Principle of Bodyes,) have any Re∣markable Power either to deprive our Tin∣cture of its Coeruleous Colour, or restore it, when upon the Affusion of Spirit of Vi∣negar it has disappear'd.

Notes

• Nicolaus Monar∣des lib. simplic. ex India allator. cap. 27.
• Kircher. Art. Mag. Ducis & umbrae, lib. 1. part. 3.