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 L.

Yet here, Pyrophilus, I must take leave to insert an Experiment, though perhaps you'l think its coming in here an Intrusion, For I confess its more proper place would have been among those Experiments, that were brought as proofs and applications of our Notions concerning the differences of

Salts; but not having remembred to insert it in its fittest place, I had rather take no∣tice of it in this, than leave it quite unmen∣tion'd: partly because it doth somewhat differ from the rest of our Experiments about Colours, in the way whereby 'tis made; and partly because the grounds upon which I devis'd it, may hint to you some∣what of the Method I use in Designing and Varying Experiments about Colours, and upon this account I shall inform you, not only What I did, but Why I did it.

I consider'd then that the work of the former Experiments was either to change the Colour of a Body into another, or quite to destroy it, without giving it a suc∣cessor, but I had a mind to give you also a way, whereby to turn a Body endued with one Colour into two Bodies, of Colours, as well as consistencies, very distinct from each other, and that by the help of a Body that had it self no Colour at all. In order to this, I remembered, that finding the Acidi∣ty of Spirit of Vinegar to be wholly de∣story'd by its working upon Minium (or calcin'd Lead) whereby the Salin parti∣cles of the Menstruum have their Taste and Nature quite alter'd, I had, among other Conjectures I had built upon that change, rightly concluded, that the Solution of Lead

in Spirit of Vinegar would alter the Colour of the Juices and Infusions of several Plants, much after the like manner that I had found Oyl of Tartar to do; and according∣ly I was quickly satisfied upon Tryal, that the Infusion of Rose-leaves would by a small quantity of this Solution well mingl'd with it, be immediately turn'd into a some∣what sad Green.

And further, I had often found, that Oyl of Vitriol, though a potently Acid Menstru∣um, will yet Praecipitate many Bodies, both Mineral and others, dissolv'd not onely in Aqua fortis (as some Chymists have ob∣serv'd) but particularly in Spirit of Vine∣gar, and I have further found, that the Calces or Powders Praecipitated by this Li∣quor were usually fair and White.

Laying these things together, 'twas not difficult to conclude, that if upon a good Tincture of Red Rose-leaves made with fair Water, I dropp'd a pretty quantity of a strong and sweet Solution of Minium, the Liquor would be turn'd into the like muddy Green Substance, as I have formerly inti∣mated to You, that Oyl of Tartar would reduce it to, and that if then I added a con∣venient quantity of good Oyl of Vitriol, this last nam'd Liquor would have two distinct operations upon the Mixture, the one, that

it would Praecipitate that resolv'd Lead in the form of a White Powder; the other, that it would Clarifie the muddy Mixture, and both restore, and exceedingly heighten the Redness of the Infusion of Roses, which vvas the most copious Ingredient of the Green composition, and accordingly trying the Experiment in a Wine glass sharp at the bottom (like an inverted Cone) that the subsiding Powder might seem to take up the more room, and be the more con∣spicuous, I found that when I had shaken the Green Mixture, that the colour'd Li∣quor might be the more equally dispersed, a few drops of the rectifi'd Oyl of Vitriol did presently turn the opacous Liquor into one that was cleer and Red, almost like a Rubie, and threw down good store of a Powder, which when 'twas settl'd, would have appear'd very White, if some inter∣spers'd Particles of the red Liquor had not a little Allay'd the Purity, though not ble∣mish'd the Beauty of the Colour. And to shew you, Pyrophilus, that these Effects do not flow from the Oyl of Vitriol, as it is such, but as it is a strongly Acid Menstruum, that has the property both to Praecipitate Lead, as well as some other Concretes out of Spirit of Vinegar, and to heighten the Colour of Red Rose-leaves, I add, that I

have done the same thing, though perhaps not quite so well with Spirit of Salt, and that I could not do it with Aqua-sortis, because though that potent Menstruum does as well as the others heighthen the Redness of Ro∣ses, yet it would not like them Precipitate Lead out of Spirit of Vinegar, but would rather have dissolv'd it, if it had not found it dissolv'd already.

And as by this way we have produc'd a Red Liquor, and a White Precipitate out of a Dirty Green magistery of Rose-leaves, so by the same Method, you may produce a fair Yellow, and sometimes a Red Li∣quor, and the like Precipitate, out of an In∣fusion of a curious Purple Colour. For you may call to mind, that in the Annotation upon the 39^th. Experiment I intimated to you, that I had with a few drops of an Alcaly turn'd the Infusion of Logg-wood into a lovely Purple. Now if instead of this Alcaly I substituted a very strong and well Filtrated Solution of Minium, made with Spirit of Vinegar, and put about half as much of this Liquor as there was of the Infusion of Logg-wood, (that the mixture might afford a pretty deal of Precipitate,) the affusion of a conventent proportion of Spirit of Salt, would (if the Liquors were well and nimbly stirr'd together) presently

strike down a Precipitate like that formerly mention'd, and turn the Liquor that swam above it, for the most part into a lovely Yellow.

But for the advancing of this Experiment a little further, I consider'd, that in case I first turn'd a spoonfull of the infusion of Logg-wood Purple, by a convenient pro∣portion of the Solution of Minium, the Af∣fusion of Spirit of Sal Armoniack, would Precipitate the Corpuscles of Lead con∣ceal'd in the Solution of Minium, and yet not destory the Purple colour of the Li∣quor; whereupon I thus proceeded; I took about a spoonfull of the fresh Tincture of Logg-wood, (for I found that if it were stale the Experiment would not alwayes succeed,) and having put to it a conveni∣ent proportion of the Solution of Minium to turn it into a deep and almost opacous Purple, I then drop'd in as much Spirit of Sal Armoniack, as I guess'd would Preci∣pitate about half or more (but not all) of the Lead, and immediately stirring the mix∣ture well together, I mingled the Precipi∣tated parts with the others, so that they fell to the bottom, partly in the form of a Pow∣der, and partly in the form of a Curdled Substance, that (by reason of the Predo∣minancy of the Ting'd Corpuscles over

the White) retain'd as well as the Super∣natant Liquor, a Blewish Purple colour sufficiently Deep, and then instantly (but yet Warily,) pouring on a pretty Quantity of Spirit of Salt, the matter first Precipita∣ted, was, by the above specifi'd figure of the bottome of the Glass preserv'd from being reach'd by the Spirituous Salt; which hastily Precipitated upon it a new Bed (if I may so call it) of White Powder, being the remaining Corpuscles of the Lead, that the Urinous Spirit had not struck down: So that there appear'd in the Glass three distinct and very differingly colour'd Sub∣stances; a Purple or Violet-colour'd Pre∣cipitate at the bottom, a White and Car∣nation (sometimes a Variously colour'd) Precipitate over That, and at the Top of all a Transparent Liquor of a lovely Yellow, or Red.

Thus you see, Pyrophilus, that though to some I may have seem'd to have lighted on this (50^th.) Experiment by chance, and though others may imagine, that to have excogitated it, must have proceeded from some extraordinary insight into the nature of Colours, yet indeed, the devising of it need not be look'd upon as any great mat∣ter, especially to one that is a little vers'd in the notions, I have in these, and other Pa∣pers

hinted concerning the differences of Salts. And perhaps I might add upon more than conjecture, that these very notions and some particulars scatteringly deliver'd in this Treatise, being skilfully put together, may suggest divers matters (at least) about Colours, that will not be altogether Despi∣cable. But those hinted, Pyrophilus, I must now leave such as You to prosecute, having already spent farr more time than I intended to allow my self in acquainting You with particular Experiments and Observations concerning the changes of Colour, to which I might have added many more, but that I hope I may have presented You with a competent number to make out in some measure what I have at the beginning of this Essay either propos'd as my Design in this Tract, or deliver'd as my Conjectures con∣cerning these matters. And it not being my present Designe, as I have more than once Declar'd, to deliver any Positive Hypothesis or solemn Theory of Colours, but only to furnish You with some Experiments to∣wards the framing of such a Theory; I shall add nothing to what I have said already, but a request that you would not be forward to think I have been mistaken in any thing I have deliver'd as matter of Fact concer∣ning the changes of Colours, in case you

should not every time you trye it, find it exactly to succeed. For besides the Contin∣gencies to which we have elsewhere shewn some other Experiments to be obnoxious, the omission or variation of a seemingly un∣considerable circumstance, may hinder the success of an Experiment, wherein no other fault has been committed. Of which truth I shall only give you that single and almost obvious, but yet illustrious instance of the Art of Dying Scarlets, for though you should see every Ingredient that is us'd a∣bout it, though I should particularly in∣form You of the weight of each, and though you should be present at the kindling of the fire, and at the increasing and remitting of it, when ever the degree of Heat is to be alter'd, and though (in a word) you should see every thing done so particular∣ly that you would scarce harbour the least doubt of your comprehending the whole Art: Yet if I should not disclose to You, that the Vessels, that immediately con∣tain the Tinging Ingredients, are to be made of or to be lin'd with Tin, You would never be able by all that I could tell you else (at least, if the Famousest and Can∣didest Artificers do not strangely delude themselves) to bring your Tincture of

Chochinele to Dye a perfect Scarlet. So much depends upon the very Vessel, where∣in the Tinging matters are boyl'd, and so great an Influence may an unheeded Circumstance have on the Success of Experiments concerning Colours.