Experiments and Considerations Touching Colours (1664) by Robert Boyle

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_EXPERIMENT XXX._

Among the Experiments that tend to shew that the change of Colours in
Bodies may proceed from the Vary'd Texture of their Parts, and the
consequent change of their Disposition to Reflect or Refract the Light,
that sort of Experiments must not be left unmention'd, which is afforded us
by Chymical Digestions. For, if _Chymists_ will believe several famous
Writers about what they call the Philosophers Stone, they must acknowledge
that the same Matter, seald up Hermetically in a Philosophical Egg, will by
the continuance of Digestion, or if they will have it so (for it is not
Material in our case which of the two it be) of Decoction, run through a
great Variety of differing Colours, before it come to that of the Noblest
_Elixir_; whether that be Scarlet, or Purple, or what ever other Kind of
Red. But without building any thing on so Obtruse and Questionable an
Operation, (which yet may be pertinently represented to those that believe
the thing) we may observe, that divers Bodies digested in carefully-clos'd
Vessels, will in tract of time, change their Colour: As I have elsewhere
mention'd my having observ'd ev'n in Rectify'd Spirit of Harts-horn, and as
is evident in the Precipitations of Amalgams of Gold, and Mercury, without
Addition, where by the continuance of a due Heat the Silver-Colour'd
Amalgam is reduc'd into a shining Red Powder. Further Instances of this
Kind you may find here and there in divers places of my other Essays. And
indeed it has been a thing, that has much contributed to deceive many
_Chymists_, that there are more Bodies than one, which by Digestion will be
brought to exhibit that Variety and Succession of Colours, which they
imagine to be Peculiar to what they call the _True matter of the
Philosophers_. But concerning this, I shall referr you to what you may
elsewhere find in the Discourse written touching the passive Deceptions of
_Chymists_, and more about the Production of Colours by Digestion you will
meet with presently. Wherefore I shall now make only this Observation from
what has been deliver'd, That in these Operations there appears not any
cause to attribute the new Colours emergent to the Action of a new
Substantial form, nor to any Increase or Decrement of either the Salt,
Sulphur, or Mercury of the Matter that acquires new Colours: For the
Vessels are clos'd, and these Principles according to the _Chymists_ are
Ingenerable and Incorruptible; so that the Effect seems to proceed from
hence, that the Heat agitating and shuffling the Corpuscles of the Body
expos'd to it, does in process of time so change its Texture, as that the
Transposed parts do Modifie the incident Light otherwise, than they did
when the Matter appear'd of another Colour.

_EXPERIMENT XXXI._

Among the several changes of Colour, which Bodies acquire or disclose by
Digestion, it it very remarkable, that _Chymists_ find a Redness rather
than any other Colour in most of the Tinctures they Draw, and ev'n in the
more Gross Solutions they make of almost all Concretes, that abound either
with Mineral or Vegetable Sulphur, though the _Menstruum_ imploy'd about
these Solutions or Tinctures be never so Limpid or Colourless.

This we have observ'd in I know not how many Tinctures drawn with Spirit of
Wine from _Jalap_, _Guaicum_, and several other Vegetables; and not only in
the Solutions of _Amber_, _Benzoin_, and divers other Concretes made with
the same _Menstruum_, but also in divers Mineral Tinctures. And, not to
urge that familiar Instance of the Ruby of Sulphur, as _Chymists_ upon the
score of its Colour, call the Solution of Flowers of Brimstone, made with
the Spirit of Turpentine, nor to take notice of other more known Examples
of the aptness of Chymical Oyls, to produce a Red Colour with the Sulphur
they extract, or dissolve; not to insist (I say) upon Instances of this
nature, I shall further represent to you, as a thing remarkable, that, both
Acid and Alcalizate Salts, though in most other cases of such contrary
Operations, in reference to Colours, will with many Bodies that abound with
Sulphureous, or with Oyly parts, produce a Red; as is manifest partly in
the more Vulgar Instances of the Tinctures, or Solutions of Sulphur made
with _Lixiviums_, either of Calcin'd Tartar or Pot-ashes, and other Obvious
examples, partly by this, that the true Glass of Antimony extracted with
some Acid Spirits, with or without Wine, will yield a Red Tincture, and
that I know an Acid Liquor, which in a moment will turn Oyl of Turpentine
into a deep Red. But among the many Instances I could give you of the easie
Production of Redness by the Operation of Saline Spirit, as well as of
Spirit of Wine; I remember two or three of those I have tried, which seem
remarkable enough to deserve to be mention'd to you apart.

_EXPERIMENT XXXII._

But before we set them down, it will not perhaps appear impertinent to
premise;

That there seems to be a manifest Disparity betwixt Red Liquors, so that
some of them may be said to have a Genuine Redness in comparison of others,
that have a Yellowish Redness: For if you take (for example) a good
Tincture of _Chochineel_, dilute it never so much with fair Water, you will
not (as far as I can judge by what I have tried) be able to make it a
Yellow Liquor. Insomuch that a Single drop of a rich Solution of
_Cochineel_ in Spirit of Urine, being Diluted with above an Ounce of fair
Water, exhibited no Yellowishness at all, but a fair (though somewhat
faint) Pinck or Carnation; and even when _Cochineel_ was by degrees Diluted
much beyond the newly mention'd Colour, by the way formerly related to you
in the twenty fourth Experiment, I remember not, that there appear'd in the
whole Trial any Yellow. But if you take Balsom of Sulphur (for Instance)
though it may appear in a Glass, where it has a good Thickness, to be of a
deep Red, yet if you shake the Glass, or pour a few drops on a sheet of
White Paper, spreading them on it with your Finger, the Balsom that falls
back along the sides of the Glass, and that which stains the Paper, will
appear Yellow, not Red. And there are divers Tinctures, such as that of
Amber made with Spirit of Wine, (to name now no more) that will appear
either Yellow or Red, according as the Vessels that they fill, are Slender
or Broad.

_EXPERIMENT XXXIII._

But to proceed to the Experiments I was about to deliver; _First_; Oyl or
Spirit of Turpentine, though clear as fair Water, being Digested upon the
purely White Sugar of Lead, has, in a short time, afforded us a high Red
Tincture, that some Artists are pleas'd to call the Balsom of _Saturn_,
which they very much (and probably not altogether without cause) extoll as
an excellent Medicine in divers Outward affections.

_EXPERIMENT XXXIV._

_Next_, take of common Brimstone finely powdred five Ounces, of
Sal-Armoniack likewise pulveriz'd an equal weight, of beaten Quick-lime six
Ounces, mix these Powders exquisitely, and Distill them through a Retort
plac'd in Sand by degrees of Fire, giving at length as intense a Heat as
you well can in Sand, there will come over (if you have wrought well) a
Volatile Tincture of Sulphur, which may probably prove an excellent
Medicine, and should have been mention'd among the other Preparations of
Sulphur, which we have elsewhere imparted to you, but that it is very
pertinent to our present Subject, The change of Colours. For though none of
the Ingredients be Red, the Distill'd Liquor will be so: and this Liquor if
it be well Drawn, will upon a little Agitation of the Vial first unstop'd
(especially if it be held in a Warmer hand) lend forth a copious Fume, not
Red, like that of Nitre, but White; And sometimes this Liquor may be so
Drawn, that I remember, not long since, I took pleasure to observe in a
parcel of it, that Ingredients not Red, did not only yield by Distillation
a Volatile Spirit that was Red, but though that Liquor did upon the bare
opening of the Bottle it was kept in, drive us away with the plenty and
sulphureous sent of a White steam which it sent forth, yet the Liquor it
self being touch'd by our Fingers, did immediately Dye them Black.

_EXPERIMENT XXXV._

The third and _last_ Experiment I shall now mention to shew, how prone
Bodies abounding in Sulphureous parts are to afford a Red Colour, is one,
wherein by the Operation of a Saline Spirit upon a White or Whitish Body,
which according to the _Chymists_ should be altogether Sulphureous, a
Redness may be produc'd, not (as in the former Experiments) slowly, but in
the twinkling of an Eye. We took then of the Essential Oyl of Anniseeds,
which has this Peculiarity, that in Cold weather it loses its Fluidity and
the greatest part of its Transparency, and looks like a White or Whitish
Oyntment, and near at hand seems to consist of a Multitude of little soft
Scales: Of this Coagulated Stuff we spread a little with a Knife upon a
piece of White Paper, and letting fall on it, and mixing with it a drop or
two of Oyl of Vitriol, immediately (as we fore-saw) there emerg'd together
with some Heat and Smoak, a Blood-Red Colour, which therefore was in a
trice produc'd by two Bodies, whereof the one had but a Whitish Colour, and
the other (if carefully rectify'd) had no Colour at all.

_EXPERIMENT XXXVI._

But on this Occasion (_Pyrophilus_) we must add once for all, that in many
of the above-recited Experiments, though the changes of Colour happen'd as
we have mention'd them: yet the emergent or produc'd Colour is oft times
very subject to Degenerate, both quickly and much. Notwithstanding which,
since the Changes, we have set down, do happen presently upon the Operation
of the Bodies upon each other, or at the times by us specify'd; _that_ is
sufficient both to justifie our Veracity, and to shew what we Intend; it
not being Essential to the Genuineness of a Colour to be Durable. For a
fading Leaf, that is ready to Rot, and moulder into Dust, may have as true
a Yellow, as a Wedge of Gold, which so obstinately resists both Time and
Fire. And the reason, why I take occasion from the former Experiment to
subjoyn this general Advertisement, is, that I have several times observ'd,
that the Mixture resulting from the Oyls of Vitriol, and of Anniseeds,
though it acquire a thicker consistence than either of the Ingredients had,
has quickly lost its Colour, turning in a very short time into a dirty
Gray, at least in the Superficial parts, where 'tis expos'd to the Air;
which last Circumstance I therefore mention, because that, though it seem
probable, that this Degeneration of Colours may oft times and in divers
cases proceed from the further Action of the Saline Corpuscles, and the
other Ingredients upon one another, yet in many cases much of the Quick
change of Colours seems ascribeable to the Air, as may be made probable by
several reasons: The first whereof may be fetcht from the newly recited
Example of the two Oyls; The next may be, that we have sometimes observ'd
long Window-Curtains of light Colours, to have that part of them, which was
expos'd to the Air, when the Window was open, of one Colour, and the lower
part, that was sheltred from the Air by the Wall, of another Colour: And
the third Argument may be fetch'd from divers Observations, both of others,
and our own; For of that Pigment so well known in Painters Shops, by the
name of _Turnsol_, our Industrious _Parkinson_, in the particular account
he gives of the Plant that bears it, tells us also, That _the Berries when
they are at their full Maturity, have within them between the outer Skin
and the inward Kirnel or Seed, a certain Juice or Moisture, which being
rubb'd upon Paper or Cloath, at the first appears of a fresh and lovely
Green Colour, but presently changeth into a kind of Blewish Purple, upon
the Cloath or Paper, and the same Cloath afterwards wet in Water, and wrung
forth, will Colour the Water into a Claret Wine Colour, and these_
(concludes he) _are those Raggs of Cloath, which are usually call'd_
Turnsol _in the Druggists or Grocers Shops_[21]. And to this Observation of
our _Botanist_ we will add an Experiment of our own, (made before we met
with That) which, though in many Circumstances, very differing, serves to
prove the same thing; for having taken of the deeply Red Juice of
_Buckthorn_ Berries, which I bought of the Man that uses to sell it to the
Apothecaries, to make their Syrrup _de Spina Cervina_, I let some of it
drop upon a piece of White Paper, and having left it there for many hours,
till the Paper was grown dry again, I found what I was inclin'd to suspect,
namely, That this Juice was degenerated from a deep Red to a dirty kind of
Greyish Colour, which, in a great part of the stain'd Paper seem'd not to
have so much as an Eye of Red: Though a little Spirit of Salt or dissolv'd
_Alcaly_ would turn this unpleasant Colour (as formerly I told you it would
change the not yet alter'd Juice) into a Red or Green. And to satisfie my
self, that this Degeneration of Colour did not proceed from the Paper, I
drop'd some of the deep Red or Crimson Juice upon a White glaz'd Tile, and
suffering it to dry on there, I found that ev'n in that Body, on which it
could not Soak, and by which it could not be Wrought, it nevertheless lost
its Colour. And these Instances (_Pyrophilus_) I am the more carefull to
mention to you, that you may not be much Surpris'd or Discourag'd, if you
should sometimes miss of performing punctually what I affirm my self to
have done in point of changing Colours; since in these Experiments the
over-sight or neglect of such little Circumstances, as in many others would
not be perhaps considerable, may occasion the mis-carrying of a Trial. And
I was willing also to take this occasion of Advertising you in the
repeating of the Experiments mention'd in this Treatise, to make use of the
Juices of Vegetables, and other things prepar'd for your Trials, as soon as
ever they are ready, lest one or other of them grow less fit, if not quite
unfit by delay; and to estimate the Event of the Trials by the Change, that
is produc'd presently upon the due and sufficient Application of Actives to
Passives, (as they speak) because in many cases the effects of such
Mixtures may not be lasting, and the newly produc'd Colour may in a little
time degenerate. But, (_Pyrophilus_) I forgot to add to the two former
Observations lately made about Vegetables, a third of the same Import, made
in Mineral substances, by telling you, That the better to satisfie a Friend
or two in this particular, I sometimes made, according to some Conjectures
of mine, this Experiment; That having dissolv'd good Silver in
_Aqua-fortis_, and Precipitated it with Spirit of Salt, upon the first
Decanting of the Liquor, the remaining Matter would be purely White; but
after it had lain a while uncover'd, that part of it, that was Contiguous
to the Air, would not only lose its Whiteness, but appear of a very Dark
and almost Blackish Colour, I say that part that was Contiguous to the Air,
because if that were gently taken off, the Subjacent part of the same Mass
would appear very White, till that also, having continu'd a while expos'd
to the Air, would likewise Degenerate. Now whether the Air perform these
things by the means of a Subtile Salt, which we elsewhere show it not to be
destitute of, or by a peircing Moisture, that is apt easily to insinuate it
self into the Pores of some Bodies, and thereby change their Texture, and
so their Colour; Or by solliciting the Avolation of certain parts of the
Bodies, to which 'tis Contiguous; or by some other way, (which possibly I
may elsewhere propose and consider) I have not now the leisure to
discourse. And for the same reason, though I could add many other
Instances, of what I formerly noted touching the emergency of Redness upon
the Digestion of many Bodies, insomuch that I have often seen upon the
Borders of _France_ (and probably we may have the like in _England_) a sort
of Pears, which digested for some time with a little Wine, in a Vessel
exactly clos'd, will in not many hours appear throughout of a deep Red
Colour, (as also that of the Juice, wherein they are Stew'd, becomes) but
ev'n on pure and white Salt of Tartar, pure Spirit of Wine, as clear as
Rock-water, will (as we elsewhere declare) by long Digestion acquire a
Redness; Though I say such Instances might be Multiply'd, and though there
be some other Obvious changes of Colours, which happen so frequently, that
they cannot but be as well Considerable as Notorious; such as is the
Blackness of almost all Bodies burn'd in the open Air: yet our haste
invites us to resign you the Exercise of enquiring into the Causes of these
Changes. And certainly, the reason both _why_ the Soots of such differing
Bodies are almost all of them all Black, _why_ so much the greater part of
Vegetables should be rather Green than of any other Colour, and
particularly (which more directly concerns this place) _why_ gentle Heats
do so frequently in Chymical Operations produce rather a Redness than
another Colour in digested _Menstruums_, not only Sulphureous, as Spirit of
Wine, but Saline, as Spirit of Vinegar, may be very well worth a serious
Inquiry; which I shall therefore recommend to _Pyrophilus_ and his
Ingenious Friends.

[21] _Parkinson_, Thea. Bot. Trib. 4 cap. 12.

_EXPERIMENT XXXVII._

It may seem somewhat strange, that if you take the Crimson Solution of
_Cochineel_, or the Juice of Black Cherries, and of some other Vegetables
that afford the like Colour, (which because many take but for a deep Red,
we do with them sometimes call it so) and let some of it fall upon a piece
of Paper, a drop or two of an Acid Spirit, such as Spirit of Salt, or
_Aqua-fortis_, will immediately turn it into a fair Red. Whereas if you
make an Infusion of Brazil in fair Water, and drop a little Spirit of Salt
or _Aqua-fortis_ into it, that will destroy its Redness, and leave the
Liquor of a Yellow, (sometimes Pale) I might perhaps plausibly enough say
on this occasion, that if we consider the case a little more attentively,
we may take notice, that the action of the Acid Spirit seems in both cases,
but to weaken the Colour of the Liquor on which it falls. And so though it
destroy Redness in the Tincture of Brazil, as well as produce Red in the
Tincture of _Chochineel_, its Operations may be Uniform enough, since as
Crimson seems to be little else than a very deep Red, with (perhaps) an Eye
of Blew, so some kinds of Red seem (as I have lately noted) to be little
else than heightned Yellow. And consequently in such Bodies, the Yellow
seems to be but a diluted Red. And accordingly Alcalizate Solutions and
Urinous Spirits, which seem dispos'd to Deepen the Colours of the Juices
and Liquors of most Vegetables, will not only restore the Solution of
_Cochineel_ and the Infusion of Brazil to the Crimson, whence the Spirit of
Salt had chang'd them into a truer Red; but will also (as I lately told
you) not only heighthen the Yellow Juice of Madder into Red, but advance
the Red Infusion of Brazil to a Crimson. But I know not whether it will not
be much safer to derive these Changes from vary'd Textures, than certain
kinds of Bodies; and you will perhaps think it worth while, that I should
add on this occasion, That it may deserve some Speculation, why,
notwithstanding what we have been observing, though Blew and Purple seem to
be deeper Colours than Red, and therefore the Juices of Plants of either of
the two former Colours may (congruously enough to what has been just now
noted) be turn'd Red by Spirit of Salt or _Aqua-fortis_, yet Blew Syrrup of
Violets and some Purples should both by Oyl of Tartar and Spirit of Urine
be chang'd into Green, which seems to be not a deeper but a more diluted
Colour than Blew, if not also than Purple.

_EXPERIMENT XXXVIII._

It would much contribute to the History of Colours, if _Chymists_ would in
their Laboratories take a heedfull notice, and give us a faithfull account
of the Colours observ'd in the Steams of Bodies either Sublim'd or
Distill'd, and of the Colours of those Productions of the Fire, that are
made up by the Coalition of those Steams. As (for Instance) we observe in
the Distilling of pure Salt peter, that at a certain season of the
Operation, the Body, though it seem either Crystalline, or White, affords
very Red Fumes: whereas though Vitriol be Green or Blew, the Spirit of it
is observ'd to come over in Whitish Fumes. The like Colour I have taken
notice of in the Fumes of several other Concretes of differing Colours, and
Natures, especially when Distill'd with strong Fires. And we elsewhere
note, that ev'n Soot, as Black as it is, has fill'd our Receivers with such
copious White Fumes, that they seem'd to have had their In-sides wash'd
with Milk. And no less observable may be, the Distill'd Liqours, into which
such Fumes convene, (for though we will not deny, that by skill and care a
Reddish Liqour may be obtain'd from Nitre) yet the common Spirit of it, in
the making ev'n of which store of these Red Fumes are wont to pass over
into the Receiver, appears not to be at all Red. And besides, that neither
the Spirit of Vitriol, nor that of Soot is any thing White; And, besides
also, that as far as I have observ'd, most (for I say not all) of the
Empyreumatical Oyls of Woods, and other Concretes, are either of a deep
Red, or of a Colour between Red and Black; besides this, I say, 'tis very
remarkable that notwithstanding that great Variety of Colours to be met
with in the Herbs, Flowers, and other Bodies wont to be Distill'd in
_Balneo_: yet (as far at least as our common Distillers Experience
reacheth) all the Waters and Spirits that first come over by that way of
Distillation, leave the Colours of their Concretes behind them, though
indeed there be one or two Vegetables not commonly taken notice of, whose
Distill'd Liqours I elsewhere observe to carry over the Tincture of the
Concrete with them. And as in Distillations, so in Sublimations, it were
worth while to take notice of what comes up, in reference to our present
scope, by purposely performing them (as I have in some cafes done) in
conveniently shap'd Glasses, that the Colour of the ascending Fumes may be
discern'd; For it may afford a Naturalist good Information to observe the
Congruities or the Differences betwixt the Colours of the ascending Fumes,
and those of the _Flowers_, they compose by their Convention. For it is
evident, that these _Flowers_, do many of them in point of Colour, much
differ, not only from one another, but oft times from the Concretes that
afforded them. Thus, (not here to repeat what I formerly noted of the Black
Soots of very differingly Colour'd Bodies) though Camphire and Brimstone
afford _Flowers_ much of their own Colour, save that those of Brimstone are
wont to be a little Paler, than the Lumps that yielded them; yet ev'n of
Red _Benzoin_, that sublim'd Substance, which _Chymists_ call its
_Flowers_, is wont to be White or Whitish. And to omit other Instances,
ev'n one and the same Black Mineral, Antimony, may be made to afford
_Flowers_, some of them Red, and some Grey, and, which is more strange,
some of them purely White. And 'tis the Prescription of some Glass-men by
exquisitely mingling a convenient proportion of Brimstone, Sal-Armoniack,
and Quicksilver, and Subliming them, together, to make a Sublimate of an
excellent Blew; and though having caus'd the Experiment to be made, we
found the produc'd Sublimate to be far from being of a lovely Colour, (as
was promis'd) that there and there, it seem'd Blewish, and at least was of
a Colour differing enough from either of the Ingredients, which is
sufficient for our present purpose. But a much finer Colour is promis'd by
some of the Empiricks, that pretend to Secrets, who tell us, that Orpiment,
being Sublim'd, will afford among the Parts of it that fly Upward, some
little Masses, which, though the Mineral it self be of a good Yellow, will
be Red enough to emulate Rubies, both in Colour and Translucency. And this
Experiment may, for ought I know, sometimes succeed; for I remember, that
having in a small Bolt-head purposely sublim'd some powder'd Orpiment, we
could in the Lower part of the Sublimate discern here and there some
Reddish Lines, though much of the Upper part of the Sublimate consisted of
a matter, which was not alone purely Yellow, but transparent almost like a
Powder. And we have also this way obtain'd a Sublimate, the Lower part
whereof though it consisted not of Rubies, yet the small pieces of it,
which were Numerous enough, were of a pleasant Reddish Colour, and
Glitter'd very prettily. But to insist on such kind of Trials and
Observations (where the ascending Fumes of Bodies differ in Colour from the
Bodies themselves) though it might indeed Inrich the History of Colours,
would Robb me of too much of the little time I have to dispatch what I have
further to tell you concerning them.

_EXPERIMENT XXXIX_

Take the dry'd Buds (or Blossoms) of the Pomegranate Tree, (which are
commonly 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
Tincture, 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 Liquor, you drop into the simple Infusion a little rectify'd
Spirit of Sea-Salt, the Pale and almost Colourless Liquor will immediately
not only grow more Transparent, but acquire a high Redness, like that of
Rich Claret Wine, which so suddenly acquir'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.

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