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 XV.

And now, Pyrophilus, it will not be impro∣per for us to take some notice of an Opinion touching the cause of Blackness, which I judged not so seasonable to Question, till I

I had set down some of the Experiments, that might justifie my dissent from it. You know that of late divers Learned Men, having adopted the three Hypostatical Principles, besides other Notions of the Chymists, are very inclinable to reduce all Qualities of Bodies to one or other of those three Principles, and Particularly assign for the cause of Blackness the Sootie steam of adust or Torrifi'd Sulphur. But I hope that what we have deliver'd above to countenance the Opinion we have pro∣pos'd about the Cause of Blackness, will so easily supply you with several Particulars that may be made use of against this Opinion, that I shall now represent to You but two things concerning it.

And First it seems that the favourers of the Chymicall Theories might have pitcht upon some more proper term, to express the Efficient of Blackness than Sulphur adust; for we know that common Sulphur, not only when Melted, but even when Sublim'd, does not grow Black by suffering the Action of the fire, but continues and ascends Yellow, and rather more than less White, than it was before its being expos'd to the fire. And if it be set on fire, as when we make that acid Liquor, that Chymists call Oleum Sulphuris per campanam, it affords

very little Soot, and indeed the flame yeelds so little, that it will scarce in any degree Black a sheet of White Paper, held a pretty while over the flame and smoak of it, which is observed rather to Whiten than Infect linnen, and which does plainly make Red Roses grow very Pale, but not at all Black, as far as the Smoak is permitted to reach the leaves. And I can shew you of a sort of fixt Sulphur made by an In∣dustrious Laborant of your acquaintance, who assur'd me that he was wont to keep it for divers weeks together night and day in a naked and Violent fire, almost like that of the Glass-house, and when, to satisfie my Curiosity, I made him take out a lump of it, though it were glowing hot (and yet not melted,) it did not, when I had suffered it to cool, appear Black, the true Colour of it being a true Red. I know it may be said, that Chymists in the Opinion above recited mean the Principle of Sulphur, and not common Sulphur which receives its name, not from its being all perfectly of a Sul∣phureous Nature, but for that plenty and Predominancy of the Sulphureous Prin∣ciple in it. But allowing this, 'tis easie to reply, that still according to this very Rea∣son, torrifi'd Sulphur should afford more Blackness, than most other concretes,

wherein that Principle is confess'd to be far less copious. Also when I have expos'd Camphire to the fire in Close Vessels, as Inflamable, and consequently (according to the Chymists) as Sulphureous a Body as it is, I could not by such a degree of Heat, as brought it to Fusion, and made it Boyl in the glass, impress any thing of Blackness, or of any other Colour, than its own pure White, upon this Vegetable concrete. But what shall we say to Spirit of Wine, which being made by a Chymical Analysis of the Liquor that affords it, and being totally Inflamable, seems to have a full right to the title they give it of Sulphur Vegetabile, & yet this fluid Sulphur not only contracts not any degree of Blackness by being often so heated, as to be made to Boyl, but when it burns away with an Actual flame, I have not found that it would discolour a piece of White Paper held over it, with any discernable Soot. Tin also, that wants not, according to the Chymists, a Sulphur Jo∣viale, when throughly burned by the fire into a Calx, is not Black, but eminently White. And I lately noted to you out of Bellonius, that the Charcoals of Oxy-cedar are not of the former of these two Colours, but of the latter. And the Smoak of our Tinby coals here in England, has been

usually observ'd, rather to Blanch linnen then to Black it. To all which, other Parti∣culars of the like nature might be added, but I rather choose to put you in mind of the third Experiment, about making Black Liquors, or Ink, of Bodies that were non of them Black before. For how can it be said, that when those Liquors are put together actually Cold, and continne so after their mixture, there intervenes any new Adustion of Sulphur to produce the emergent Blackness? (and the same question will be appliable to the Blackness produc'd upon the blade of a Knife, that has cut Lem∣mons and some kind of Sowr apples, if the juyce (though both Actually and Poten∣tially Cold) be not quickly wip'd of) And when by the instilling either of a few drops of Oyl of Vitriol as in the second Experi∣ment, or of a little of the Liquor mention'd in the Passage pointed at in the fourth Experiment, (where I teach at once to Destroy one black Ink, and make another) the Blackness produc'd by those Experi∣ments is presently destroy'd; if the Colour proceeded only from the Plenty of Sulphu∣rous parts, torrify'd in the Black Bodies, I demand, what becomes of them, when the Colour so suddenly dissappears? For it can∣not Reasonably be said, that all those that

suffic'd to make so great a quantity of Black Matter, should resort to so very small a proportion of the Clarifying Liquor, (if I may so call it) as to be deluted by it, with out at all Denigrating it. And if it be said that the Instill'd Liquor dispers'd those Black Corpuscles, I demand, how that Dispersion comes to destroy their Blackness, but by making such a Local Motion of their part, as destroys their former Texture? which may be a Matter of such moment in cases like ours, that I remember that I have in few houres, without addition, from Soot it self, attain'd pretty store of Crystalline Salt, and good store of Transparent Li∣quor, and (which I have on another occasi∣on noted as remarkable) this so Black sub∣stance had its Colour so alter'd, by the change of Texture it receiv'd from the fire, wherewith it was distill'd, that it did for a great while afford such plenty of very white Exhalations, that the Receiver, though large, seem'd to be almost fill'd with Milk.

Secondly, But were it granted, as it is in some cases not Improbable, that divers Bodies may receive a Blackness from a Sootie Exhalation̄, occasion'd by the Adustion of their Sulphur, which (for the Reasons lately mention'd I should rather call their Oyly parts;) yet still this account

is applicable but to some Particular Bodies, and will afford us no General Theory of Blackness. For if, for example, White Harts-horn, being, in Vessels well luted to each other, expos'd to the fire, be said to turn Black by the Infection of its own Smoak, I think I may justly demand, what it is that makes the Smoak or Soot it self Black, since no such Colour, but its con∣trary, appear'd before in the Harts-horn? And with the same Reason, when we are told, that torrify'd Sulphur makes bodies Blakc, I desire to be told also, why Tor∣refaction makes Sulphur it self Black? nor will there be any Satisfactory Reason assign'd of these Quaeries, without taking in those Fertile as well as Intelligible Mechani∣cal Principles of the Position and Texture of the Minute parts of the body in reference to the Light and the Eye; and these appli∣cable Principles may serve the turn in many cases, where the Adustion of Sulphur can∣not be pretended; as in the appearing Blackness of an Open window, lookt upon at a somewhat remote distance from the house, as also in the Blackness Men think they see in the Holes that happen to be in White linnen, or Paper of the like Colour; and in the Increasing Blackness immediatly Produc'd barely by so rubbing Velvet,

whose Piles were Inclin'd before, as to re∣duce them to a more Erected posture, in which and in many other cases formerly alleg'd, there appears nothing requisite to the Production of the Blackness, but the hindering of the incident Beams of Light from rebounding plentifully enough to the Eye. To be short, those I reason with, do concerning Blackness, what the Chymists are wont also to do concerning other Qua∣lities, namely to content themselves to tell us, in what Ingredient of a Mixt Bo∣dy, the Quality enquir'd after, does reside, instead of explicating the Nature of it, which (to borrow a comparison from their own Laboratories) is much as if in an enquiry after the cause of Salivation, they should think it enough to tell us, that the several Kinds of Praecipitates of Gold and Mercury, as likewise of Quick-silver and Silver (for I know that make and use of such Praecipitates also) do Salivate upon the account of the Mercury, which though Disguis'd abounds in them, whereas the Difficulty is as much to know upon what account Mercury it self, rather than other Bodies, has that power of working by Sali∣vation. Which I say not, as though it were not something (and too often the most we can arrive at) to discover in which of the

Ingredients of a Compounded Body, the Quality, whose Nature is fought, resides, but because, though this Discovery it self may pass for something, and is oftentimes more than what is taught us about the same subjects in the Schools, yet we ought not to think it enough, when more Clear and Particular accounts are to be had.