Experiments and Considerations Touching Colours (1664) by Robert Boyle

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_EXPERIMENT XXII._

Our next Experiment (_Pyrophilus_) will perhaps seem to be of a contrary
Nature to the two former, made upon Syrrup of Violets, and Juice of
Blew-bottles. For as in them by the Affusion of Oyl of Tartar, a Blewish
Liquor is made Green, so in this, by the sole Mixture of the same Oyl, a
Greenish Liquor becomes Blew. The hint of this Experiment was given us by
the practice of some _Italian_ Painters, who being wont to Counterfeit
_Ultra-marine Azure_ (as they call it) by Grinding Verdigrease with
Sal-Armoniack, and some other Saline Ingredients, and letting them Rot (as
they imagine) for a good while together in a Dunghill, we suppos'd, that
the change of Colour wrought in the Verdigrease by this way of Preparation,
must proceed from the Action of certain Volatile and Alcalizate Salts,
abounding in some of the mingled Concretes, and brought to make a further
Dissolution of the Copper abounding in the Verdigrease, and therefore we
Conjectur'd, that if both the Verdigrease, and such Salts were dissolv'd in
fair Water, the small Parts of both being therein more subdivided, and set
at liberty, would have better access to each other, and thereby Incorporate
much the more suddenly; And accordingly we found, that if upon a strong
Solution of good French Verdigrease (for 'tis that we are wont to imploy,
as the best) you pour a just quantity of Oyl of Tartar, and shake them well
together, you shall immediately see a notable Change of Colour, and the
Mixture will grow thick, and not transparent, but if you stay a while, till
the Grosser part be Precipitated to, and setled in the Bottom, you may
obtain a clear Liquor of a very lovely Colour, and exceeding delightfull to
the Eye. But, you must have a care to drop in a competent Quantity of Oyl
of Tartar, for else the Colour will not be so Deep, and Rich; and if
instead of this Oyl you imploy a clear _Lixivium_ of Pot-ashes, you may
have an Azure somewhat Lighter or Paler than, and therefore differing from,
the former. And if instead of either of these Liquors, you make use of
Spirit of Urine, or of Harts-horn, you may according to the Quantity and
Quality of the Spirit you pour in, obtain some further Variety (though
scarce considerable) of Caeruleous Liquors. And yet lately by the help of
this Urinous Spirit we made a Blew Liquor, which not a few Ingenious
Persons, and among them, some, whose Profession makes them very Conversant
with Colours, have looked upon with some wonder. But these Azure Colour'd
Liquors should be freed from the Subsiding matter, which the Salts of
Tartar or Urine precipitate out of them, rather by being Decanted, than by
Filtration. For by the latter of these ways we have sometimes found, the
Colour of them very much Impair'd, and little Superiour to that of the
grosser Substance, that it left in the Filtre.

_EXPERIMENT XXIII._

That Roses held over the Fume of Sulphur, may quickly by it be depriv'd of
their Colour, and have as much of their Leaves, as the Fume works upon,
burn'd pale, is an Experiment, that divers others have tried, as well as I.
But (_Pyrophilus_) it may seem somewhat strange to one that has never
consider'd the Compounded nature of Brimstone, That, whereas the Fume of
Sulphur will, as we have said, Whiten the Leaves of Roses; That Liquor,
which is commonly call'd Oyl of Sulphur _per Campanam_, because it is
suppos'd to be made by the Condensation of these Fumes in Glasses shap't
like Bells, into a Liquor, does powerfully heighten the Tincture of Red
Roses, and make it more Red and Vivid, as we have easily tried by putting
some Red-Rose Leaves, that had been long dried, (and so had lost much of
their Colour) into a Vial of fair Water. For a while after the Affusion of
a convenient Quantity of the Liquor we are speaking of, both the Leaves
themselves, and the Water they were Steep'd in, discover'd a very fresh and
lovely Colour.

_EXPERIMENT XXIV._

It may (_Pyrophilus_) somewhat serve to Illustrate, not only the Doctrine
of _Pigments_, and of _Colours_, but divers other Parts of the _Corpuscular
Philosophy_; as that explicates Odours, and many other things, not as the
Schools by Aery Qualities, but by Real, though extremely Minute Bodies; to
examine, how much of a Colourless Liquor, a very small Parcel of a Pigment
may Imbue with a _discernable_ Colour. And though there be scarce any thing
of Preciseness to be expected from such Trials, yet I presum'd, that (at
least) I should be able to show a much further Subdivision of the Parts of
Matter into _Visible_ Particles, than I have hitherto found taken notice
of, and than most men would imagine; no Body, that I know of, having yet
attempted to reduce this Matter to any Measure.

The Bodies, the most promising for such a purpose, might seem to be the
Metalls, especially Gold, because of the Multitude, and Minuteness of its
Parts, which might be argu'd from the incomparable Closeness of its
Texture: But though we tried a Solution of Gold made in _Aqua Regia_ first,
and then in fair Water; yet in regard we were to determine the Pigment we
imploy'd, not by _Bulk_ but _Weight_, and because also, that the Yellow
Colour of Gold is but a faint one in Comparison of the deep Colour of
_Cochineel_, we rather chose this to make our Trials with. But among divers
of these it will suffice to set down one, which was carefully made in
Vessels conveniently Shap'd; (and that in the presence of a Witness, and an
Assistant) the Sum whereof I find among my _Adversaria_, Registred in the
following Words. To which I shall only premise, (to lessen the wonder of so
strange a diffusion of the Pigment) That _Cochineel_ will be better
Dissolv'd, and have its Colour far more heightn'd by Spirit of Urine, than
(I say not by common Water, but) by Rectify'd Spirit of Wine it self.

The Note I spoke off is this. [One Grain of _Cochineel_ dissolv'd in a
pretty Quantity of Spirit of Urine, and then dissolv'd further by degrees
in fair Water, imparted a discernable, though but a very faint Colour, to
about six Glass-fulls of Water, each of them containing about forty three
Ounces and an half, which amounts to above a hundred twenty five thousand
times its own Weight.]

_EXPERIMENT XXV._

It may afford a considerable Hint (_Pyrophilus_) to him, that would improve
the Art of Dying, to know what change of Colours may be produc'd by the
three several sorts of Salts already often mention'd, (some or other of
which may be procur'd in Quantity at reasonable Rates) in the Juices,
Decoctions, Infusions, and (in a word) the more soluble parts of
Vegetables. And, though the design of this Discourse be the Improvement of
Knowledge, not of Trades: yet thus much I shall not scruple to intimate
here, That the Blew Liquors, mention'd in the twentieth and one and
twentieth Experiments, are far from being the only Vegetable Substances,
upon which Acid, Urinous, and Alcalizate Salts have the like Operations to
those recited in those two Experiments. For Ripe _Privet Berries_ (for
instance) being crush'd upon White Paper, though they stain it with a
Purplish Colour, yet if we let fall on some part of it two or three drops
of Spirit of Salt, and on the other part a little more of the Strong
Solution of Pot-ashes, the former Liquor immediately turn'd that part of
the Thick juice or Pulp, on which it fell, into a lovely Red, and the
latter turn'd the other part of it into a delightfull Green. Though I will
not undertake, that those Colours in that Substance shall not be much more
Orient, than Lasting; and though (_Pyrophilus_) this Experiment may seem to
be almost the same with those already deliver'd concerning Syrrup of
Violets, and the Juice of Blew-bottles, yet I think it not amiss to take
this Occasion to inform you, that this Experiment reaches much farther,
than perhaps you yet imagine, and may be of good Use to those, whom it
concerns to know, how Dying Stuffs may be wrought upon by Saline Liquors.
For, I have found this Experiment to succeed in so many Various Berries,
Flowers, Blossoms, and other finer Parts of Vegetables, that neither my
Memory, nor my Leisure serves me to enumerate them. And it is somewhat
surprizing to see, by how Differingly-colour'd Flowers, or Blossoms, (for
example) the Paper being stain'd, will by an Acid Spirit be immediately
turn'd Red, and by any _Alcaly_ or any Urinous Spirit turn'd Green;
insomuch that ev'n the crush'd Blossoms of _Meserion_, (which I gather'd in
Winter and frosty Weather) and those of Pease, crush'd upon White Paper,
how remote soever their Colours be from Green, would in a moment pass into
a deep Degree of that Colour, upon the Touch of an Alcalizate Liquor. To
which let us add, That either of those new Pigments (if I may so call them)
may by the Affusion of enough of a contrary Liquor, be presently chang'd
from Red into Green, and from Green into Red, which Observation will hold
also in Syrrup of Violets, Juices of Blew-bottles, &c.

_Annotation._

After what I have formerly deliver'd to evince, That there are many
Instances, wherein new Colours are produc'd or acquir'd by Bodies, which
_Chymists_ are wont to think destitute of Salt, or to whose change of
Colours no new Accession of Saline Particles does appear to contribute, I
think we may safely enough acknowledge, that we have taken notice of so
many Changes made by the Intervention of Salts in the Colours of Mix'd
Bodies, that it has lessen'd our Wonder, That though _many Chymists_ are
wont to ascribe the Colours of Such Bodies to their Sulphureous, and _the
rest_ to their Mercurial Principle; yet _Paracelsus_ himself directs us in
the Indagation of Colours, to have an Eye principally upon Salts, as we
find in that passage of his, wherein he takes upon him to Oblige his
Readers much by Instructing them, of what things they are to expect the
Knowledge from each of the three distinct Principles of Bodies. _Alias_
(says he) _Colorum similis ratio est: De quibus brevem institutionem hanc
attendite, quod scilicet colores omnes ex Sale prodeant. Sal enim dat
colorem, dat Balsamum._[19] And a little beneath. _Iam natura Ipsa colores
protrathit ex sale, cuique speciei dans illum, qui ipsi competit_, &c.
After which he concludes; _Itaque qui rerum omnium corpora cognoscere vult,
huic opus est, ut ante omnia cognoscat Sulphur, Ab hoc, qui desiderat
novisse Colores is scientiam istorum petat a Sale, Qui scire vult Virtutes,
is scrutetur arcana Mercurii. Sic nimirum fundamentum hauserit Mysteriorum,
in quolibet crescenti indagandorum, prout natura cuilibet speciei ea
ingessit_. But though _Paracelsus_ ascribes to each of his belov'd
Hypostatical Principles, much more than I fear will be found to belong to
it; yet if we please to consider Colours, not as _Philosophers_, but as
_Dyers_, the concurrence of Salts to the striking and change of Colours,
and their Efficacy, will, I suppose, appear so considerable, that we shall
not need to quarrel much with _Paracelsus_, for ascribing in this place
(for I dare not affirm that he uses to be still of one Mind) the Colours of
Bodies to their Salts, if by Salts he here understood, not only Elementary
Salts, but such also as are commonly taken for Salts, as Allom, Crystals of
Tartar, Vitriol, &c. because the Saline principle does chiefly abound in
them, though indeed they be, as we elsewhere declare, mix'd Bodies, and
have most of them, besides what is Saline, both Sulphureous, Aqueous, and
Gross or Earthy parts.

[19] Paracelsus de Mineral. tract. 1. pag. m. 243

But though (_Pyrophilus_) I have observ'd a Red and Green to be produc'd,
the former, by Acid Salts, the later by Salts not Acid, in the express
Juices of so many differing Vegetable Substances, that the Observation, if
persued, may prove (as I said) of good Use: yet to show you how much e'vn
these Effects depend upon the particular Texture of Bodies, I must subjoyn
some cases wherein I (who am somewhat backwards to admit Observations for
Universal) had the Curiosity to discover, that the Experiments would not
Uniformly succeed, and of these Exceptions, the chief that I now remember,
are reducible to the following three.

_EXPERIMENT XXVI._

And, (first) I thought fit to try the Operation of Acid Salts upon
Vegetable Substances, that are already and by their own Nature Red. And
accordingly I made Trial upon Syrrup of Clove-july-flowers, the clear
express'd Juice of the succulent Berries of _Spina Cervina_, or Buckthorn
(which I had long kept by me for the sake of its deep Colour) upon Red
Roses, Infusion of Brazil, and divers other Vegetable Substances, on some
of which crush'd (as is often mention'd) upon White Paper, (which is also
to be understood in most of these Experiments, if no Circumstance of them
argue otherwise) Spirit of Salt either made no considerable Change, or
alter'd the Colour but from a Darker to a Lighter Red. How it will succeed
in many other Vegetable Juices, and Infusions of the same Colour, I have at
present so few at hand, that I must leave you to find it out your self. But
as for the Operation of the other sorts of Salts upon these Red Substances,
I found it not very Uniform, some Red, or Reddish Infusions, as of Roses,
being turn'd thereby into a dirty Colour, but yet inclining to Green. Nor
was the Syrrup of Clove-july-flowers turn'd by the solution of Pot-ashes to
a much better, though somewhat a Greener, Colour. Another sort of Red
Infusions was by an _Alcaly_ not turn'd into a Green, but advanc'd into a
Crimson, as I shall have occasion to note ere long. But there were other
sorts, as particularly the lovely Colour'd juice of Buckthorn Berries, that
readily pass'd into a lovely Green.

_EXPERIMENT XXVII._

Among other Vegetables, which we thought likely to afford Exceptions to the
General Observation about the differing Changes of Colours produc'd by Acid
and Sulphureous Salts, we thought fit to make Trial upon the Flowers of
_Jasmin_, they being both White as to Colour, and esteem'd to be of a more
Oyly nature than other Flowers. Whereupon having taken the White parts only
of the Flowers, and rubb'd them somewhat hard with my Finger upon a piece
of clean Paper, it appear'd very little Discolour'd. Nor had Spirit of
Salt, wherewith I moisten'd one part of it, any considerable Operation upon
it. But Spirit of Urine, and somewhat more effectually a strong Alcalizate
Solution, did immediately turn the almost Colourless Paper moisten'd by the
Juice of the _Jasmin_, not as those Liquors are wont to do, when put upon
the Juices of other Flowers, of a good Green, but of a Deep, though
somewhat Greenish Yellow, which Experiment I did afterwards at several
times repeat with the like success. But it seems not that a great degree of
Unctuousness is necessary to the Production of the like Effects, for when
we try'd the Experiment with the Leaves of those purely White Flowers that
appear about the end of Winter, and are commonly call'd _Snow drops_, the
event, was not much unlike that, which, we have been newly mentioning.

_EXPERIMENT XXVIII._

Another sort of Instances to show, how much changes of Colour effected by
Salts, depend upon the particular Texture of the Colour'd Bodies, has been
afforded me by several _Yellow_ Flowers, and other Vegetables, as Mary-gold
Leaves, early Prim-roses, fresh Madder, &c. For being rubb'd upon White
Paper, till they imbued it with their Colour, I found not, that by the
addition of Alcalizate Liquors, nor yet by that of an Urinous Spirit, they
would be turn'd either Green or Red: nor did so Acid a Spirit, as that of
Salt, considerably alter their Colour, save that it seem'd a little to
Dilute it. Only in some early Prim-roses it destroy'd the greatest part of
the Colour, and made the Paper almost White agen. And Madder also afforded
some thing peculiar, and very differing from what we have newly mention'd:
For having gather'd Some Roots of it, and, (whilst they were recent)
express'd upon White Paper the Yellow Juice, an Alcalizate Solution drop'd
upon it did not turn it either Green or White, but Red. And the bruis'd
Madder it self being drench'd with the like Alcalizate Solution, exchang'd
also its Yellowishness for a Redness.

_An admonition touching the four preceding Experiments._

Having thus (_Pyrophilus_) given you divers Instances, to countenance the
General observation deliver'd in the twenty fifth Experiment, and divers
Exceptions whereby it ought to be Limited; I must leave the further Inquiry
into these Matters to your own Industry. For not remembring at present many
of those other Trials, long since made to satisfie my self about
Particulars, and not having now the Opportunity to repeat them, I must
content my Self to have given you the Hint, and the ways of prosecuting the
search your Self; and only declare to you in general, that, As I have made
many Trials, unmention'd in this Treatise, whose Events were agreeable to
those mention'd in the twenty fifth Experiment, so (to name now no other
Instances) what I have try'd with Acid and Sulphureous Salts upon the Pulp
of Juniper Berries, rubb'd upon White Paper, inclines me to think, That
among that vast Multitude, and strange Variety of Plants that adorn the
face of the Earth, perhaps many other Vegetables may be found, on which
such _Menstruums_ may not have such Operations, as upon the Juice of
Violets, Pease-blossoms, &c. no nor upon any of those three other sorts of
Vegetables, that I have taken notice of in the three fore-going
Experiments. It sufficiently appearing ev'n by these, that the effects of a
Salt upon the Juices of particular Vegetables do very much depend upon
their particular Textures.

_EXPERIMENT XXIX._

It may be of some Use towards the discovery of the nature of these Changes,
which the Alimental Juice receives in some Vegetables, according to the
differing degrees of their Maturity, and according to the differing kinds
of Plants of the same Denomination, to observe what Operation Acid,
Urinous, and Alcalizate Salts will have upon the Juices of the several
sorts of the Vegetable substances I have been mentioning.

To declare my meaning by an Example, I took from the same Cluster, one
Blackberry full Ripe, and another that had not yet gone beyond a Redness,
and rubbing apiece of white Paper, with the former, I observ'd, that the
Juice adhering to it was of adark Reddish Colour, full of little Black
Specks; and that this Juice by a drop of a strong _Lixivium_, was
immediately turn'd into a Greenish Colour deep enough, by as much Urinous
Spirit into a Colour much of Kin to the former, though somewhat differing,
and fainter; and by a drop of Spirit of Salt into a fine and lightsome Red:
where as the Red Berry being in like manner rubb'd upon Paper, left on it a
Red Colour, which was very little alter'd by the Acid Spirit newly nam'd,
and by the Urinous and Lixiviate Salts receiv'd changes of Colour differing
from those that had been just before produc'd in the dark Juice of the Ripe
Blackberry.

I remember also, that though the Infusion of Damask-Roses would as well,
though not so much, as that of Red, be heightned by Acid Spirits to an
intense degree of Redness, and by Lixiviate Salts be brought to a Darkish
Green; yet having for Trials sake taken a Rose, whose Leaves, which were
large and numerous, like those of a Province Rose, were perfectly Yellow,
though in a Solution of Salt of Tartar, they afforded a Green Blewish
Tincture, yet I did not by an Acid Liquor obtain a Red one; all that the
Saline Spirit I imploy'd, perform'd, being (if I much misremember not) to
Dilute Somewhat the Yellowness of the Leaves. I would also have tried the
Tincture of Yellow Violets, but could procure none. And if I were in those
Islands of _Banda_, which are made Famous as well as Rich, by being the
almost only places, where Cloves will prosper, I should think it worth my
Curiosity to try, what Operation the three differing Kinds of Salts, I have
so often mention'd, would have upon the Juice of this Spice, (express'd at
the several Seasons of it) as it grows upon the Tree. Since good Authors
inform us, (of what is remarkable) that these whether Fruits, or Rudiments
of Fruits, are at first _White_, afterward _Green_, and then _Reddish_,
before they be beaten off the Tree, after which being Dry'd before they are
put up, they grow _Blackish_ as we see them. And one of the recentest
_Herbarists_ informs us, that the Flower grows upon the top of the Clove it
self, consisting of four small Leaves, like a Cherry Blossom, but of an
excellent _Blew_. But (_Pyrophilus_) to return to our own Observations, I
shall add, that I the rather choose, to mention to you an Example drawn
from Roses, because that though I am apt to think, as I elsewhere
advertise, that something may be guess'd at about some of the Qualities of
the Juices of Vegetables, by the Resemblance or Disparity that we meet with
in the Changes made of their Colours, by the Operation of the same kinds of
Salts; yet that those Conjectures should be very warily made, may appear
among other things, by the Instance I have chosen to give in Roses. For
though, (as I formerly told you) the Dry'd Leaves, both of the Damask, and
of Red ones, give a Red Tincture to Water sharpen'd with Acid Salts, yet
the one sort of Leaves is known to have a Purgative faculty,[20] and the
other are often, and divers ways, imploy'd for Binding.

[20] See _Parkinson_ Th. Boran. Trib. 9. cap. 26.

And I also choose (_Pyrophilus_) to subjoyn this twenty ninth Experiment to
those that precede it, about the change of the Colours of Vegetables by
Salts, for these two reasons: The first, that you may not easily entertain
Suspitions, if in the Trials of an Experiment of some of the Kinds formerly
mention'd, you should meet with an Event somewhat differing from what my
Relations may have made you expect. And the second, That you may hereby be
invited to discern, that it may not be amiss to take notice of the
particular Seasons wherein you gather the Vegetables which in Nicer
Experiments you make use of. For, it I were not hindred both by haste and
some justifiable Considerations, I could perhaps add considerable
Instances, to those lately deliver'd, for the making out of this
Observation; but for certain reasons I shall at present substitute a
remarkable passage to be met with in that Laborious Herbarist Mr.
_Parkinson_, where treating of the Virtues of the (already divers times
mention'd) Buckthorn Berries, he subjoyns the following account of several
Pigments that are made of them, not only according to the several ways of
Handling them, but according to the differing Seasons of Maturity, at which
they are Gather'd; _Of these Berries_, (says he) _are made three several
sorts of Colours as they shall be gather'd, that is, being gather'd while
they are Green, and kept Dry, are call'd Sapberries, which being steep'd
into some Allom-water, or fresh bruis'd into Allom-water, they give a
reasonable fair Yellow Colour which Painters use for their Work, and
Book-binders to Colour the edges of Books, and Leather-dressers to Colour
Leather, as they use also to make a Green Colour, call'd Sap-green, taken
from the Berries when they are Black, being bruis'd and put into a Brass or
Copper Kettle or Pan, and there suffer'd to abide three or four_ _Days, or
a little heated upon the Fire, and some beaten Allom put unto them, and
afterwards press'd forth, the Juice or Liquor is usually put in great
Bladders tied with strong thred at the Head and hung up untill it be Dry,
which is dissolv'd in Water or Wine, but Sack_ (he affirms) _is the best to
preserve the Colour from Starving, (as they call it) that is, from
Decaying, and make it hold fresh the longer. The third Colour (where of
none_ (says he) _that I can find have made mention but only_ Tragus_) is a
Purplish Colour, which is made of the Berries suffer'd to grow upon the
Bushes untill the middle or end of_ November, _that they are ready to drop
from the Trees._

And, I remember (_Pyrophilus_) that I try'd, with a success that pleas'd me
well enough, to make such a kind of Pigment, as Painters call Sap-green, by
a way not unlike that, deliver'd here by our Author, but I cannot now find
any thing relating to that matter among my loose Papers. And my Trials were
made so many years ago, that I dare not trust my Memory for Circumstances,
but will rather tell you, that in a noted Colour-shop, I brought them by
Questions to confess to me, that they made their Sap-green much after the
ways by our _Botanist_ here mention'd. And on this occasion I shall add an
Observation, which though it does not strictly belong to this place, may
well enough be mention'd here, namely, that I find by an account given us
by the Learned _Clusius_, of _Alaternus_, that ev'n the Grosser Parts of
the same Plant, are some of them one Colour, and some another; For speaking
of that Plant, he tells us, that the _Portugalls_ use the Bark to Dye their
Nets into a Red Colour, and with the Chips of the Wood, which are Whitish,
they Dye a Blackish Blew.

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