PHYSICS. affirmed as matter of fact, feems to be true, in moft cafes, but not in all. For tho' it be a common obfervation among dyers, that cloth, which has once been thoroughly imbued with black, cannot well afterwards be dyed of a lighter colour; yet the experiments, lately delivered, may fhew, that, were the change of colour in black bodies attempted, not by mixing thofe of lighter colours with them, but by adding fuch things, as are proper to alter the texture of thofe corpufcles, which contain the black; 'tis no difficult matter to effect. For inks of feveral kinds, may immediately be deprived of all their blacknefs; and thofe made with log-wood, and red rofes, be changed, the one into a red, the other into a reddish liquor. With oil of vitriol, I have fometimes turn'd black pieces of filk into a kind of yellow; and tho' the taffaty were thereby made rotten, yet that no way prejudices the experiment; the change of black filk, into yellow, being never the lefs true, because the yellow filk is not good. And as for whitenefs, I think the general affirmation of its being fo eafily deftroyed, or tranfmuted, by any other colour, ought not to be received, without fome cautions, and reftrictions. For tho, according to what I formerly noted, lead is, by calcination, turn'd into that red powder, called minium; and tin, by the fame means, reduced to a white calx; yet the common putty, inftead of being, as it is pretended, and ought to be, only the calx of tin, is, by the artificers who make it, to fave the charge of that metal, compofed but of half tin, and half lead, if not far more lead than tin; and yet the putty, in fpight of fo much lead, is a very white powder, without difclofing any mixture of minium. And fo, if you take two parts of copper, which is a high-coloured metal, and but one of tin, you may, by fufion, bring them into a mass, wherein the whitenefs of the tin is much more confpicuous, and predominant, than the reddishness of the copper. And a very honeft man affures me upon his own experience, that if arfenic and copper be melted together in a due proportion, the arfenic will blanch the copper both within and without; and that this white mixture, skilfully kept upon the cupel, would prefently let go its arfenic, which made whitenefs its predominant colour, and return to the reddishness of copper: fo that fome white mineral bodies may be very capable of eclipfing others, and of making their colour predominant in mixtures. And, as a further confirmation of this, I remember, that I had a lump of filver and gold, melted together, wherein, by the estimate of a very experienced refiner, there might be about a third part of gold; yet the yellow colour of that metal was fo hid, that the whole mals appeared to be filver; and, when rubbed upon the touch-ftone, 'twas not easily diftinguished from the touch of common filver: tho' if I put a little Aqua fortis, upon any part of the white furface it had given the touch-ftone, the filver, in the moistened part, being immediately taken up, and conceal'd by the liquor, the golden particles would prefently difclose themfelves, and look as if pure gold alone had been rubbed upon the ftone. 15. Having not 15. Having fcraped a piece of black horn, with a piece of glass, into ma- PHYSICS. ny thin curled fhavings, and laid a quantity of them together; I found, that the heap they compofed, was white: and tho' if I laid it on a clean piece of white paper, its colour feem'd fomewhat eclipfed by the greater whitenefs of that body; yet if I laid it upon any thing very black, it appeared to be of a good white. This cafy experiment feems very oppofite to Colours depen their doctrine, who would have colours flow from the fubftantial forms on the Subftantial forms of of bodies; and that of the chymifts alfo, who afcribe them to one, or bodies. other, of the three hypoftatical principles: for tho', in our cafe, there was fo great a change made, that the fame body, without being, fubftantially, either increas'd, or leffen'd, paffes immediately from one extreme colour to another, even from black to white; yet this fo great and fudden change, is effected by a flight mechanical tranfpofition of parts; there being no falt, fulphur, or mercury, added, or taken away; nor any fubitantial form generated, and deftroyed; the effect proceeding only from a local motion of the parts: which fo vary'd their pofition, as to multiply their diftinct furfaces, and qualify them to reflect far more light to the eye, than they could before they were fcraped off from the entire body of the black horn. doctrine of 16. The chymifts, we know, ufually affign, for the caufe of black- The chymical nefs, the fuliginous fteams of aduft fulphur; but many of the preceding blackness con experiments will abundantly confute this doctrine. If they here mean the futed. fumes of common fulphur, 'tis proper to remind them, that fufion, or fublimation, does not turn that fubftance black; but it thereby becomes rather more than lefs white; and, when fired, it affords fo little foot, as fcarce, in any degree, to blacken white paper; but the fmoke of it rather blanches linen, and turns red rofes pale. Befides, I have feen a fixed kind of fulphur kept, for many weeks together, in a very violent fire, that did not, when cool'd, appear black, but of a true red. If, by fulphur, they mean the fulphureous principle; upon this fuppofition, torrify'd fulphur fhould afford more blackness, than most other concretes; wherein that principle is fuppofed more deficient. Yet fpirit of wine, tho totally inflammable, will not, by burning, difcolour white paper, held over it; and the fmoke of our Tinby coals has been found, rather to blanch, than blacken linen. To thefe particulars, many others, of the fame kind, might be added; but we need only look back, for further fatisfaction, to our way of making black inks, from substances of different colours; for how can it be faid, that, when the component liquors thereof are put together, actually cold, and continue fo, after their mixture, there intervenes any new aduftion of fulphur, to produce the emergent blacknefs? And when, by inftilling a few drops of oil of vitriol, &c. the blackness, produced in thofe experiments, is prefently deftroy'd; if the colour proceeded only from the fulphureous parts, torrify'd, in the black bodies, I demand, what becomes of them, when the colour fo fuddenly disappears? for it cannot reafonably be faid, that all thofe which fufficed to make fo great a quantity of black matter, fhould VOL. II. refort H PHYSICS. refort to fo very fmall a proportion of the clarifying liquor, and be diluted by it, without giving it any blacknefs. And if it be faid, that the inftilled liquor difperfed thofe black corpufcles; I demand how that dif perfion comes to deftroy their blacknefs, but by fuch a local motion of their parts, as deftroys their former texture? This may be a matter of fuch moment, in cafes like ours, that I remember I have, in a few hours, without addition, from foot itfelf, obtain'd a large quantity of crystalline falt, and of a tranfparent liquor; yet this black fubftance had its colour fo altered, by the change of its texture from the fire wherewith it was diftilled, that it did, for a great while, afford fuch plenty of very white exhalations, that the receiver, tho' large, feem'd to be almost fill'd with milk. Secondly, But were it granted, as it is in fome cafes not improbable, that bodies may receive a blackness from a footy exhalation, occafion'd by the aduftion of their fulphur, or oily parts; yet this is applicable only to fome particular bodies, and will afford us no general theory of blacknefs. For if, for example, white hart's-horn, included in veffels well luted to each other, and expofed to the fire, be faid to turn black, by the infection of its own fmoke; I think I may juftly demand, what makes the fmoke, or foot itfelf, black, fince no fuch colour appeared before in the hart's-horn? And, with the fame reafon, when we are told, that torrify'd fulphur makes bodies black; I defire to be told alfo, why torrifaction makes fulphur itself black? Nor will there be any fatisfactory reafon affigned of thefe queries, without taking in thofe intelligible mechanical principles of the pofition and texture of the minute parts of the body, with regard to the light and the eye; which may ferve the turn, in many cafes, where the aduftion of fulphur cannot be pretended; as in the apparent blacknefs of an open window, view'd at a a diftance, &c. in which, and many other cafes, formerly alledged, there appears nothing requifite to the production of blacknefs, but a prevention of the incident rays of light, from being plentifully enough reflected to the eye. In fhort, the doctrine I here oppofe, is pleaded for, as chymifts commonly argue about qualities; who content themfelves to fay in ་་ For the production of black, Sir Ifaac" particles of thefe, by reason of their Newton obferves, that "the corpufcles of" very great number, easily overfpreading "the body must be much less than any" the grofs particles of others; why glafs, "of thofe which exhibit colours. For" ground very elaborately with fand, on "at all greater fizes, there is too much" a copper-plate, till it be well polished, light reflected, to conftitute blacknefs." makes the fand, together with what is And from hence, fays he, may be un-" worn off from the glafs and copper, be"derfood, why fire, and the more fubtile" come very black; why black fubftances "diffolver, putrefaction, by dividing the" do fooneft, of all others, become hot particles of fubftances, turn them to" in the fun's light, and burn; confiderblack; why fmall quantities of black" ing the multitude of refractions in a fubftances impart their colour very free-" little room, and the easy commotion "ly, and intenfely, to other fubftances," of fuch very finall corpufcles, ." See to which they are applied; the minute! Newton. Optic. p.235. what what ingredient of a mixed body a particular quality refides, instead of PHYSICS. explaining its nature. SECT. III. Here propofe to throw together the miscellaneous experiments I have made, with relation to colours. I know of no way more likely to convince the generality of men, how Many changes of colour produ great a fhare the variable texture of bodies may have, in making themed by one fimple appear of differing colours, than by fhewing how the addition of a fingle ingredient. ingredient, that either is colourlefs, or at least has not any of the colours to be produced, is immediately able, by introducing a fecret change of texture, to make the body 'tis put to, appear fometimes fo one colour, fometimes of another; according as the parts of the body wrought upon, are difpofed to receive fuch a change, as modifies the incident rays of light, after the manner requifite to make them exhibit a blue, a green, a red, or fome other particular colour. For this end, I made choice of the fpirit of falt, as that which is very fimple; and which, if it be not too highly rectified, may be had clear, and colourless. With this fpirit, I proceeded to make the following experiments, upon feveral bodies, whofe differing textures feem'd to fit them for my purpose. 1. Some drops of well-coloured fyrup of violets, being let fall together upon a piece of white paper; if a third, or fourth part fo much fpirit of falt be mixed with them, the fyrup will presently become of a red colour, ufually inclining to purple. 2. But if the liquor to be acted on, be otherwife difpofed, 'tis poffible, with fpirit of falt, to turn it from a blue colour, not to a red, but to a green; as I have fometimes done, by letting fall into a deep folution of filings of copper, made with an urinous fpirit, as that of fal-armoniac, juft as many drops of fpirit of falt, as were requifite to produce the change intended. A very fmall error, either in excefs, or defect, may leave the mixture ftill blue, or bring it to be colourlefs. 3. Upon a few drops of good fyrup of violets, let fall two or three drops of good fpirit of urine, hart's-horn, or the like; and when, by mixing them well, the fyrup has acquired a fine green colour; by putting to it a little of the fpirit of falt, and ftirring it, you may turn the green fyrup into a red. 4. If you put a quantity of red rofe-leaves, well dried, into a glafs vial, almoft full of fair water; and, foon after, put to them as much spirit of falt as will make the water pretty fharp; you will quickly fee, both that liquor, and the contained leaves, brought to a fine lovely red, which they will long retain. The like effect fpirit of falt will have on fome other vegetables of a ftiptic, or of an aftringent nature. 5. But if, by infufing brazil-wood in fair water, you make a tincture of it, which you may much deepen,by dropping into it a little fpirit of hart'shorn, or of urine; and you then put to it a little fpirit of falt, it will pre H 2 fently PHYSICS. fently change from a deep reddish colour, to a colour far more pale, or rather yellow; fo that the fame fpirit acting upon two vegetable tinctures, differently difpofed, draws out, and heightens rednefs in the one, and destroys it in the other. 6. If you make an infufion of true Lignum Nephriticum, in fpring water, it will appear of a deep colour, like that of an orange, when you place the vial between the window and your eye; and of a fine deep blue, when you look on it with your eye placed between it and the window: but if you shake into this liquor a few drops of spirit of falt, the blue colour will presently vanish, and appear no more, in what light foever you view the vial; tho' the liquor will ftill retain the orange-colour. 7. We took common writing-ink, and having let fall feveral drops of it upon a piece of white paper; fo that, when it grew dry in the air, fome parts of the ink lay thick, and fome thinner, upon the paper, whereon it fpread itfelf: we then put a few drops of ftrong fpirit of falt, fome on one part of the black'd paper, and fome on another; and obferved, that in thofe places, where the fpirit had been put, or to which it reached, the blacknefs was quite deftroyed, and was fucceeded by an unpleasant kind of colour, that feem'd, for the moft part, to participate of yellow and blue, neither of them good in kind. 8. If in fpirit of falt, you diffolve filings of fteel, and flowly evaporate the filtred folution, it will shoot into a kind of Vitriolum Martis, which appears green, as well as that which chymifts vulgarly make with oil of vitriol. And if you take these cryftals, made with fpirit of falt, and, when they are dry, keep them in a crucible; you will find, that even a moderate fire, if duly apply'd, will make them, in a fhort time, exchange their green colour for a red, like that of the finer fort of Crocus Martis: as, indeed, this operation makes them referable to that fort of medicine. 9. We took fome mercury, precipitated per fe; and tho' crude mercury is not, as far as I have tried, foluble in our English fpirit of falt; yet this red precipitate readily diffolved in that liquor, without at all imparting its own colour to it. I alfo found, that red lead, being boil'd a while in good fpirit of falt, the rednefs totally disappear'd. So that the fame agent which produces rednefs in feveral bodies, in our two cafes quite abolish'd it. Thus alfo, the reddeft coral being diffolved in our menftruum, the redness vanishes, and the folution appears colourlefs. 10. Take fmall filings of copper, and having poured thereon good fpirit of falt, till it fwim, about two fingers breadth over them; keep the vial in a pretty ftrong fand-heat, till you perceive the menftruum has diffolved a competent part of the metal: then warily take out the vial, and holding it between your eye and the light, you will perceive the folution of copper to be of a dark and troubled colour, often inclining to a deep, but muddy red. But if you pour this folution into a wide-mouth'd glass, and let it stand for a competent time, the expofed liquor will appear of a green, much finer than that of the cryftals of iron. Take |