Experiments and Considerations Touching Colours (1664) by Robert Boyle

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_EXPERIMENT XVI._

And here, _Pyrophilus_, since we are treating of Emphatical Colours, we
shall add what we think not unworthy your Observation, and not unfit to
afford some Exercise to the Speculative. For there are some Liquors, which
though Colourless themselves, when they come to be Elevated, and Dispers'd
into Exhalations, exhibit a conspicuous Colour, which they lose again, when
they come to be Reconjoyn'd into a Liquor, as good Spirit of _Nitre_; or
upon its account strong _Aqua-fortis_, though devoid of all appearance of
Redness whilst they continue in the form of a Liquor, if a little Heat
chance to turn the Minute parts of them into Vapour, the Steam will appear
of a Reddish or deep Yellow Colour, which will Vanish when those
Exhalations come to resume the form of Liquor.

And not only if you look upon a Glass half full of _Aqua-fortis_, or Spirit
of _Nitre_, and half full of _Nitrous_ steams proceeding from it, you will
see the Upper part of the Glass of the Colour freshly mention'd, if through
it you look upon the Light. But which is much more considerable, I have
tried, that putting _Aqua-fortis_ in a long clear Glass, and adding a
little Copper or some such open Metall to it, to excite Heat and Fumes, the
Light trajected through those Fumes, and cast upon a sheet of White Paper,
did upon that appear of the Colour that the Fumes did, when directly Look'd
upon, as if the Light were as well Ting'd in its passage through these
Fumes, as it would have been by passing through some Glass or Liquor in
which the same Colour was Inherent.

To which I shall further add, that having sometimes had the Curiosity to
observe whether the Beams of the Sun near the Horizon trajected through a
very Red Sky, would not (though such rednesses are taken to be but
Emphatical Colours) exhibit the like Colour, I found that the Beams falling
within a Room upon a very White Object, plac'd directly opposite to the
Sun, disclos'd a manifest Redness, as if they had pass'd through a Colour'd
_Medium_.

_EXPERIMENT XVII._

The emergency, _Pyrophilus_, of Colours upon the Coalition of the Particles
of such Bodies as were neither of them of the Colour of that Mixture
whereof they are the Ingredients, is very well worth our attentive
Observation, as being of good use both Speculative and Practical; For much
of the Mechanical use of Colours among Painters and Dyers, doth depend upon
the Knowledge of what Colours may be produc'd by the Mixtures of Pigments
so and so Colour'd. And (as we lately intimated) 'tis of advantage to the
contemplative Naturalist, to know how many and which Colours are Primitive
(if I may so call them) and Simple, because it both eases his Labour by
confining his most sollicitous Enquiry to a small Number of Colours upon
which the rest depend, and assists him to judge of the nature of particular
compounded Colours, by shewing him from the Mixture of what more Simple
ones, and of what Proportions of them to one another, the particular Colour
to be consider'd does result. But because to insist on the Proportions, the
Manner and the Effects of such Mixtures would oblige me to consider a
greater part of the Painters Art and Dyers Trade, than I am well acquainted
with, I confin'd my self to make Trial of _several ways to produce Green_,
by the composition of Blew and Yellow. And shall in this place both
Recapitulate most of the things I have Dispersedly deliver'd already
concerning that Subject, and Recruit them.

And first, whereas Painters (as I noted above) are wont to make Green by
tempering Blew and Yellow, both of them made into a soft Consistence, with
either Water or Oyl, or some Liquor of Kin to one of those two, according
as the Picture is to be Drawn with those they call _water Colours_, or
those they term _Oyl Colours_, I found that by choosing fit Ingredients,
and mixing them in the form of Dry Powders, I could do, what I could not if
the Ingredients were temper'd up with a Liquor; But the Blew and Yellow
Powders must not only be finely Ground, but such as that the Corpuscles of
the one may not be too unequal to those of the other, lest by their
Disproportionate Minuteness the Smaller cover and hide the Greater. We us'd
with good success a slight Mixture of the fine Powder of Bise, with that of
Orpiment, or that of good Yellow Oker, I say a _slight_ Mixture, because we
found that an _exquisite_ Mixture did not do so well, but by lightly
mingling the two Pigments in several little Parcels, those of them in which
the Proportion and Manner of Mixture was more Lucky, afforded us a good
Green.

2. We also learn'd in the Dye-houses, that Cloth being Dy'd Blew with Woad,
is afterwards by the Yellow Decoction of _Luteola_ or Woud-wax or Wood-wax
Dy'd into a Green Colour.

3. You may also remember what we above Related, where we intimated, that
having in a Darkn'd Room taken two Bodies, a Blew and a Yellow, and cast
the Light Reflected from the one upon the other, we likewise obtain'd a
Green.

4. And you may remember, that we observ'd a Green to be produc'd, when in
the same Darkn'd Room we look'd at the Hole at which alone the Light
enter'd, through the Green and Yellow parts of a sheet of Marbl'd Paper
laid over one another.

5. We found too, that the Beams of the Sun being trajected through two
pieces of Glass, the one Blew and the other Yellow, laid over one another,
did upon a sheet of White paper on which they were made to fall, exhibit a
lovely Green.

6. I hope also, that you have not already forgot, what was so lately
deliver'd, concerning the composition of a Green, with a Blew and Yellow;
of which most Authors would call the one a _Real_, and the other an
_Emphatical_.

7. And I presume, you may have yet fresh in your memory, what the
fourteenth Experiment informs you, concerning the exhibiting of a Green, by
the help of a Blew and Yellow, that were both of them Emphatical.

8. Wherefore we will proceed to take notice, that we also devis'd a way of
trying whether or no Metalline Solutions though one of them at least had
its Colour Adventitious, by the mixture of the _Menstruum_ employ'd to
dissolve it, might not be made to compound a Green after the manner of
other Bodies. And though this seem'd not easie to be perform'd by reason of
the Difficulty of finding Metalline Solutions of the Colour requisite, that
would mix without Praecipitating each other; yet after a while having
consider'd the matter, the first Tryal afforded me the following
Experiment. I took a High Yellow Solution of good Gold in _Aqua-Regis_,
(made of _Aqua-fortis_, and as I remember half its weight of Spirit of
Salt) To this I put a due Proportion of a deep and lovely Blew Solution of
Crude Copper, (which I have elsewhere taught to be readily Dissoluble in
strong Spirit of Urine) and these two Liquors though at first they seem'd a
little to Curdle one another, yet being throughly mingl'd by Shaking, they
presently, as had been Conjectur'd, united into a Transparent Green Liquor,
which continu'd so for divers days that I kept it in a small Glass wherein
'twas made, only letting fall a little Blackish Powder to the Bottom. The
other _Phaenomena_ of this Experiment belong not to this place, where it may
suffice to take notice of the Production of a Green, and that the
Experiment was more than once repeated with Success.

9. And lastly, to try whether this way of compounding Colours would hold
ev'n in Ingredients actually melted by the Violence of the Fire, provided
their Texture were capable of safely induring Fusion, we caus'd some Blew
and Yellow Ammel to be long and well wrought together in the Flame of a
Lamp, which being Strongly and Incessantly blown on them kept them in some
degree of Fusion, and at length (for the Experiment requires some Patience
as well as Skil) we obtain'd the expected Ammel of a Green Colour.

I know not, _Pyrophilus_, whether it be worth while to acquaint you with
the ways that came into my Thoughts, whereby in some measure to explicate
the first of the mention'd ways of making a Green; for I have sometimes
Conjectur'd, that the mixture of the Bise and the Orpiment produc'd a Green
by so altering the Superficial Asperity, which each of those Ingredients
had apart, that the Light Incident on the mixture was Reflected with
differing Shades, as to Quantity, or Order, or both, from those of either
of the Ingredients, and such as the Light is wont to be Modify'd with, when
it Reflects from Grass, or Leaves, or some of those other Bodies that we
are wont to call Green. And sometimes too I have doubted, whether the
produced Green might not be partly at least deriv'd from this, That the
Beams that Rebound from the Corpuscles of the Orpiment, giving one kind of
stroak upon the _Retina_, whose Perception we call Yellow, and the Beams
Reflected from the Corpuscles of the Bise, giving another stroak upon the
same _Retina_, like to Objects that are Blew, the Contiguity and Minuteness
of these Corpuscles may make the Appulse of the Reflected Light fall upon
the _Retina_ within so narrow a Compass, that the part they Beat upon being
but as it were a Physical point, they may give a Compounded stroak, which
may consequently exhibit a Compounded and new Kind of Sensation, as we see
that two Strings of a Musical Instrument being struck together, making two
Noises that arrive at the Ear at the same time as to Sense, yield a Sound
differing from either of them, and as it were Compounded of both; Insomuch
that if they be Discordantly ton'd, though each of them struck apart would
yield a Pleasing Sound, yet being struck together they make but a Harsh and
troublesome Noise. But this not being so fit a place to prosecute
Speculations, I shall not insist, neither upon these Conjectures nor any
others, which the Experiment we have been mentioning may have suggested to
me. And I shall leave it to you, _Pyrophilus_, to derive what Instruction
you can from comparing together the Various ways whereby a Yellow and a
Blew can be made to Compound a Green. That which I now pretend to, being
only to shew that the first of those mention'd ways, (not to take at
present notice of the rest) does far better agree with our Conjectures
about Colours, than either with the Doctrine of the Schools, or with that
of the _Chymists_, both which seem to be very much Disfavour'd by it.

For first, since in the Mixture of the two mention'd Powders I could by the
help of a very excellent _Microscope_ (for ordinary ones will scarce serve
the turn) discover that which seem'd to the naked Eye a Green Body, to be
but a heap of Distinct, though very small Grains of Yellow Orpiment and
Blew Bise confusedly enough Blended together, it appears that the Colour'd
Corpuscles of either kind did each retain its own Nature and Colour; By
which it may be guess'd, what meer Transposition and Juxtaposition of
Minute and Singly unchang'd Particles of Matter can do to produce a new
Colour; For that this Local Motion and new Disposition of the small parts
of the Orpiment did Intervene is much more manifest than it is easie to
Explicate how they should produce this new Green otherwise than by the new
Manner of their being put together, and consequently by their new
Disposition to Modifie the Incident Light by Reflecting it otherwise than
they did before they were Mingl'd together.

Secondly, The Green thus made being (if I may so speak) Mechanically
produc'd, there is no pretence to derive it from I know not what
incomprehensible Substantial Form, from which yet many would have us
believe that Colours must flow; Nor does this Green, though a Real and
Permanent, not a Phantastical and Vanid Colour, seem to be such an Inherent
Quality as they would have it, since not only each part of the Mixture
remains unalter'd in Colour, and consequently of a differing Colour from
the Heap they Compose, but if the Eye be assisted by a _Microscope_ to
discern things better and more distinctly than before it could, it sees not
a Green Body, but a Heap of Blew and Yellow Corpuscles.

And in the third place, I demand what either Sulphur, or Salt, or Mercury
has to do in the Production of this Green; For neither the Bise nor the
Orpiment were indu'd with that Colour before, and the bare Juxtaposition of
the Corpuscles of the two Powders that work not upon each other, but might
if we had convenient Instruments be separated, unalter'd, cannot with any
probability be imagin'd either to Increase or Diminish any of the three
Hypostatical Principles, (to which of them soever the _Chymists_ are
pleas'd to ascribe Colours) nor does there here Intervene so much as Heat
to afford them any colour to pretend, that at least there is made an
Extraversion (as the _Helmontians_ speak) of the Sulphur or of any of the
two other supposed Principles; But upon this Experiment we have already
Reflected enough, if not more than enough for once.

_EXPERIMENT XVIII._

But here, _Pyrophilus_, I must advertise you, that 'tis not every Yellow
and every Blew that being mingl'd will afford a Green; For in case one of
the Ingredients do not Act only as endow'd with such a Colour, but as
having a power to alter the Texture of the Corpuscles of the other, so as
to Indispose them to Reflect the Light, as Corpuscles that exhibit a Blew
or a Yellow are wont to Reflect it, the emergent Colour may be not Green,
but such as the change of Texture in the Corpuscles of one or both of the
Ingredients qualifies them to shew forth; as for instance, if you let fall
a few Drops of Syrrup of Violets upon a piece of White Paper, though the
Syrrup being spread will appear Blew, yet mingling with it two or three
Drops of the lately mention'd Solution of Gold, I obtain'd not a Green but
a Reddish mixture, which I expected from the remaining Power of the Acid
Salts abounding in the Solution, such Salts or Saline Spirits being wont,
as we shall see anon, though weakn'd, so to work upon that Syrrup as to
change it into a Red or Reddish Colour. And to confirm that for which I
allege the former Experiment, I shall add this other, that having made a
very strong and high-colour'd Solution of Filings of Copper with Spirit of
Urine, though the _Menstruum_ seem'd Glutted with the Metall, because I put
in so much Filings that many of them remain'd for divers days Undissolv'd
at the Bottom, yet having put three or four Drops of Syrrup of Violets upon
White Paper, I found that the deep Blew Solution proportionably mingl'd
with this other Blew Liquor did not make a Blew mixture, but, as I
expected, a fair Green, upon the account of the Urinous Salt that was in
the _Menstruum_.

_EXPERIMENT XIX._

To shew the _Chymists_, that Colours may be made to Appear or Vanish, where
there intervenes no Accession or Change either of the Sulphureous, or the
Saline, or the Mercurial principle (as they speak) of Bodies: I shall not
make use of the Iris afforded by the Glass-prism, nor of the Colours to be
seen in a fair Morning in those drops of Dew that do in a convenient manner
Reflect and Refract the Beams of Light to the Eye; But I will rather mind
them of what they may observe in their own Laboratories, namely, that
divers, if not all, Chymical Essential Oyls, as also good Spirit of Wine,
being shaken till they have good store of Bubbles, those Bubbles will (if
attentively consider'd) appear adorn'd with various and lovely Colours,
which all immediately Vanish, upon the relapsing of the Liquor that affords
those Bubbles their Skins, into the rest of the Oyl, or Spirit of Wine, so
that a Colourless Liquor may be made in a trice to exhibit variety of
Colours, and may lose them in a moment without the Accession or Diminution
of any of its Hypostatical Principles. And, by the way, 'tis not unworthy
our notice, that some Bodies, as well Colourless, as Colour'd, by being
brought to a great Thinness of parts, acquire Colours though they had none
before, or Colours differing from them they were before endued with: For,
not to insist on the Variety of Colours, that Water, made somewhat
Glutinous by Sope, acquires, when 'tis blown into such Sphaerical Bubbles as
Boys are wont to make and play with; Turpentine (though it have a Colour
deep enough of its own) may (by being blown into after a certain manner) be
brought to afford Bubbles adorn'd with variety of Orient Colours, which
though they Vanish after some while upon the breaking of the Bubbles, yet
they would in likelihood always exhibit Colours upon their _Superfices_,
(though not always the same in the same Parts of them, but Vary'd according
to the Incidence of the Sight, and the Position of the Eye) if their
Texture were durable enough: For I have seen one that was Skill'd at
fashioning Glasses by the help of a Lamp, blowing some of them so strongly
as to burst them, whereupon it was found, that the Tenacity of the Metall
was such, that before it broke it suffer'd it self to be reduc'd into Films
so extremely thin, that being kept clean they constantly shew'd on their
Surfaces (but after the manner newly mention'd) the varying Colours of the
Rain-bow, which were exceedingly Vivid, as I had often opportunity to
observe in some, that I caus'd purposely to be made, to keep by me.

But lest it should be objected, that the above mentioned Instances are
drawn from Transparent Liquors, it may possibly appear, not impertinent to
add, what I have sometimes thought upon, and several times tried, when I
was considering the Opinions of the _Chymists_ about Colours, I took then a
Feather of a convenient Bigness and Shape, and holding it at a fit distance
betwixt my Eye and the Sun when he was near the Horizon, me thought there
appear'd to me a Variety of little Rain-bows, with differing and very vivid
Colours, of which none was constantly to be seen in the Feather; the like
_Phaenomenon_ I have at other times (though not with altogether so good
success) produc'd, by interposing at a due distance a piece of Black
Ribband betwixt the almost setting Sun and my Eye, not to mention the
Trials I have made to the same purpose, with other Bodies.

_EXPERIMENT XX._

Take good Syrrup of Violets, Impraegnated with the Tincture of the flowers,
drop a little of it upon a White Paper (for by that means the Change of
Colour will be more conspicuous, and the Experiment may be practis'd in
smaller Quantities) and on this Liquor let fall two or three drops of
Spirit either of Salt or Vinegar, or almost any other eminently Acid
Liquor, and upon the Mixture of these you shall find the Syrrup immediatly
turn'd Red, and the way of Effecting such a Change has not been unknown to
divers Persons who have produc'd the like, by Spirit of Vitriol, or juice
of Limmons, but have Groundlessly ascrib'd the Effect to some Peculiar
Quality of those two Liquors, whereas, (as we have already intimated)
almost any Acid Salt will turn Syrrup of Violets Red. But to improve the
Experiment, let me add what has not (that I know of) been hitherto
observ'd, and has, when we first shew'd it them, appear'd something
strange, even to those that have been inquisitive into the Nature of
Colours; namely, that if instead of Spirit of Salt, or that of Vinegar, you
drop upon the Syrrup of Violets a little Oyl of Tartar _per Deliquium_, or
the like quantity of Solution of Potashes, and rubb them together with your
finger, you shall find the Blew Colour of the Syrrup turn'd in a moment
into a perfect Green, and the like may be perform'd by divers other
Liquors, as we may have occasion elsewhere to Inform you.

_Annotation upon the twentieth Experiment_.

The use of what we lately deliver'd concerning the way of turning Syrrup of
Violets, Red or Green, may be this; That, though it be a far more common
and procurable Liquor than the Infusion of _Lignum Nephriticum_, it may yet
be easily substituted in its Room, when we have a mind to examine, whether
or no the Salt predominant in a Liquor or other Body, wherein 'tis Loose
and Abundant, belong to the Tribe of _Acid_ Salts or not. For if such a
Body turn the Syrrup of a Red or Reddish Purple Colour, it does for the
most part argue the Body (especially if it be a distill'd Liquor) to abound
with Acid Salt. But if the Syrrup be made Green, that argues the
Predominant Salt to be of a Nature repugnant to that of the Tribe of Acids.
For, as I find that either Spirit of Salt, or Oyl of Vitriol, or
_Aqua-fortis_, or Spirit of Vinegar, or Juice of Lemmons, or any of the
Acid Liquors I have yet had occasion to try, will turn Syrrup of Violets,
of a _Red_, (or at least, of a _Reddish_ Colour, so I have found, that not
only the Volatile Salts of all Animal Substances I have us'd, as Spirit of
Harts-horn, of Urine, of Sal-Armoniack, of Blood, &c. but also all the
Alcalizate Salts I have imploy'd, as the Solution of Salt of Tartar, of
Pot-ashes, of common Wood-ashes, Lime-water, &c. will immediately change
the Blew Syrrup, into a perfect Green. And by the same way (to hint that
upon the by) I elsewhere show you, both the changes that Nature and Time
produce, in the more Saline parts of some Bodies, may be discover'd, and
also how ev'n such Chymically prepar'd Bodies, as belong not either to the
Animal Kingdome, or to the Tribe of _Alcali's_, may have their new and
superinduc'd Nature successfully Examin'd. In this place I shall only add,
that not alone the Changing the Colour of the Syrrup, requires, that the
Changing Body be more strong, of the Acid, or other sort of Salt that is
Predominant in it, than is requisite for the working upon the Tincture of
_Lignum Nephriticum_; but that in this is also, the Operation of the
formerly mention'd Salts upon our Syrrup, differs from their Operation upon
our Tinctures, that in this Liquor, if the Caeruleous Colour be _Destroy'd_
by an Acid Salt, it may be _Restor'd_ by one that is either Volatile, or
Lixiviate; whereas in Syrrup of Violets, though one of these contrary Salts
will _destroy_ the Action of the other, yet neither of them will _restore_
the Syrrup to its native Blew; but each of them will Change it into the
Colour which it self doth (if I may so speak) affect, as we shall have
Occasion to show in the Notes on the twenty fifth Experiment.

_EXPERIMENT XXI._

There is a Weed, more known to Plowmen than belov'd by them, whose Flowers
from their Colour are commonly call'd _Blew-bottles_, and _Corn-weed_ from
their Growing among Corn[18]. These Flowers some Ladies do, upon the
account of their Lovely Colour, think worth the being Candied, which when
they are, they will long retain so fair a Colour, as makes them a very fine
Sallad in the Winter. But I have try'd, that when they are freshly
gather'd, they will afford a Juice, which when newly express'd, (for in
some cases 'twill soon enough degenerate) affords a very deep and pleasant
Blew. Now, (to draw this to our present Scope) by dropping on this fresh
Juice, a little Spirit of Salt, (that being the Acid Spirit I had then at
hand) it immediately turn'd (as I predicted) into a Red. And if instead of
the Sowr Spirit I mingled with it a little strong Solution of an Alcalizate
Salt, it did presently disclose a lovely Green; the same Changes being by
those differing sorts of Saline Liquors, producible in this _Natural
juice_, that we lately mention'd to have happen'd to that _factitious
Mixture_, the Syrrup of Violets. And I remember, that finding this Blew
Liquor, when freshly made, to be capable of serving in a Pen for an Ink of
that Colour, I attempted by moistning one part of a piece of White Paper
with the Spirit of Salt I have been mentioning, and another with some
Alcalizate or Volatile Liquor, to draw a Line on the leisurely dry'd Paper,
that should, e'vn before the Ink was dry, appear partly Blew, partly Red,
and partly Green: But though the latter part of the Experiment succeeded
not well, (whether because Volatile Salts are too Fugitive to be retain'd
in the Paper, and Alcalizate ones are too Unctuous, or so apt to draw
Moisture from the Air, that they keep the Paper from drying well) yet the
former Part succeeded well enough; the Blew and Red being Conspicuous
enough to afford a surprizing Spectacle to those, I acquaint not with (what
I willingly allow you to call) the _Trick_.

[18] _Herbarists_ are wont to call this Plant _Cyanus vulgaris minor_.

_Annotation upon the one and twentieth Experiment._

But lest you should be tempted to think (_Pyrophilus_) that Volatile or
Alcalizate Salts change Blews into Green, rather upon the score of the
easie Transition of the former Colour into the latter, than upon the
account of the Texture, wherein most Vegetables, that afford a Blew, seem,
though otherwise differing, to be Allied, I will add, that when I purposely
dissolv'd Blew Vitriol in fair Water, and thereby imbu'd sufficiently that
Liquor with that Colour, a Lixiviate Liquor, and a Urinous Salt being
Copiously pour'd upon distinct Parcels of it, did each of them, though
perhaps with some Difference, turn the Liquor not Green, but of a deep
Yellowish Colour, almost like that of Yellow Oker, which Colour the
Precipitated Corpuscles retain'd, when they had Leisurely subsided to the
Bottom. What this Precipitated Substance is, it is not needfull now to
Enquire in this place, and in another, I have shown you, that
notwithstanding its Colour, and its being Obtainable from an Acid
_Menstruum_ by the help of Salt of Tartar, it is yet far enough from being
the true Sulphur of Vitriol.

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