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what ingredient of a mixed body a particular quality refides, inftead of PHYSICS. explaining its nature.

SECT. III.

Here propofe to throw together the mifcellaneous experiments I have

made, with relation to colours.

I know of no way more likely to convince the generality of men, how Many changes great a fhare the variable texture of bodies may have, in making them ap. of colour propear of differing colours, than by fhewing how the addition of a fingle fimple ingrediduced by one ingredient, that either is colourless, or at least has not any of the colours ent. to be produced, is immediately able, by introducing a fecret change of texture, to make the body 'tis put to, appear fometimes of one colour, fometimes of another; according as the parts of the body wrought upon, are difpofed to receive such 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 colourlefs. 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 so much spirit 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 difposed, '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 colourless.

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 stirring it, you may turn the green fyrup into a red.

If you put a quantity of red rofe-leaves, well dried, into a glass vial, almost 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 spirit 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

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fently

PHYSICS. fently change from a deep reddish colour, to a colour far more pale, or rather yellow; fo that the fame spirit 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 fpirit of falt, the blue colour will presently vanifh, 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 ic 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 most 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 fhoot 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 thefe 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 short 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 spirit 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 spirit of falt, the redness totally disappear'd. So that the fame agent which produces redness in several bodies, in our two cafes quite abolish'd it. Thus alfo, the reddeft coral being diffolved in our menftruum, the rednefs vanishes, and the folution appears colourless.

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.

11. But if you pour this folution into a wide-mouth'd glafs, and let it ftand for a competent time, the expofed liquor will appear of a green, much finer than that of the cryftals of iron.

12. Take the clear limpid folution of filver, or of mercury, made in PHYSICS. Aqua fortis, and drop upon it fome fpirit of falt; and you will find the clear liquor turn'd white as milk, which, after a while, will let fall a precipitate of the fame colour.

13. And if, instead of a folution of filver, or quick-filver, you take a red folution, or tincture, of benjamin, or of the refinous part of jalap root; you'll also have, upon the affufion of spirit of falt, a white liquor, and a precipitate of the fame colour.

14. Being defirous to produce two differing colours at once, by the fame affufion of fpirit of falt; I infused fome dry'd red rofe-leaves in fair water, till it had acquired a deep colour from them: to this infusion, poured off warily, that it might be clear, I added a confiderable proportion of the fweet liquor, made by digefting fpirit of vinegar upon red lead; by which I knew 'twould be turn'd of a bluish green. Upon this almoft opake liquor, I pour'd fpirit of falt, which precipitated the lead that had been diffolved in the fweet liquor, into a very white powder, and gave the remaining liquor, well impregnated with particles of the rofe-leaves, a very fine and durable fcarlet colour. And if the experiment be well made, you may barely, by fhaking together, and confounding the white powder with the red liquor, make a carnation-colour, which will appear very fine and lovely, whilft it lafts; but, in no long time, the two fubftances that compofe it, feparate, by degrees, and appear each in its former place and colour.

15. We took fome fpirit of falt, that, having laid long upon filings of copper, had loft the muddy tincture it firft acquired, by being almost boil'd upon them. This liquor, that look'd like common water, we pour'd into a small wide-mouth'd cryftal glafs, and leaving it in a window, it appeared, in forty minutes, to have acquired a colour, much like that of a German amethyft; and feem'd to have no tendency to greenness. But in about three hours time, it appear'd of a lovely green.

16. Precipitate a strong folution of fublimate made in fair water, with a fufficient quantity of oil of tartar, per deliquium; put the liquor and powder into a filtre of cap-paper, and when the water is run thorough, the precipitate will remain in the filtre; which is to be flowly dry'd. Then. take it out of the filtre, in the form of a grofs powder, and having put it into a clear glafs, let fall on it, warily, fome drops of ftrong fpirit of falt; and, during the conflict that will be made, the little lumps of the precipitate will lofe all their former brick-duft colour, and turn white; tho' afterwards they will appear diffolved into a transparent liquor, wherein the orange-colour is quite abolished.

17. Having calcined copper, without any addition, but of fire and water; we took a quantity of it, and having poured thereon about three or four times its quantity of good fpirit of falt, we obtain'd a muddy reddish Tiquor, and a white powder, whofe quantity bore a confiderable proportion to the part that was diffolved; in which part itself, by the affufion of common water, and the action of the air, we afterwards produced more than one change of colour. 18. We

PHYSICS.

18. We fometimes took a fpoonful of the dark brown, or somewhat reddish folution of copper; and having put it into a cylindrical vial, that the change of colour might appear the better, we poured on it two or three spoons-ful of highly rectify'd vinous fpirit; and giving the glass a fhake, to mingle them, we prefently had a lovely green liquor; which, when well fettled, was very fair, and look'd as if it were a liquid emerald.

19. Having moiften'd a small part of fome green taffaty-ribband, twice or thrice, with good spirit of falt, we fuffer'd it to dry of itself, which it did in a fhort time; and then found, that the part wetted was no longer of a green, but a blue colour. The fame fpirit presently turn'd that part of a piece of black ribband, upon which we put two or three drops of it, to a colour not unlike what is call'd Fueille morte.

20. 'Tis ufual to fee books covered with paper, that looks fometimes of a greenish blue colour, bordering upon purple; and fometimes upon that of violets. The deeper coloured paper of this fort, I have feveral times held in one hand, and with the other lightly touched it here and there with the end of a feather, dipped in fpirit of falt; which almoft in the twinkling of an eye, dy'd the touched parts of the paper of a lovely red, that would fometimes long continue very vivid. And if, instead of a feather, I used a brush, dipt in the faline fpirit, and made many drops at once fall upon the paper; 'twas pleasant to see how fuddenly it would be fpeck

led.

21. Upon well-powdered antimony, we pour'd three or four times its weight of good spirit of falt; and caufed it to be boiled in this liquor, in a glafs veffel, wherein a part of it was diffolved, and taken up into the menftruum; when the antimony quite loft its blackness. And this fpirit of falt, thus impregnated, being dropped into fair water, the black mineral immediately fubfided, in the form of a very white powder or precipitate.

Hence, by the way, it were not amifs, if phyficians, chymifts, &c. who compound drugs, or other ingredients, would be lefs forward than they usually are, to jumble feveral of them together either unneceffarily, or without a due regard to their qualities, in refpect of one another. For most of us are but too liable to be mistaken, when we prefume before-hand to fay what changes the coalition, or other affociations of differing bodies fhall produce; efpecially if they be either faline, or plentifully partake of a faline nature: fince experience frequently fhews, that by the action and re-action confequent upon untry'd ways of compofition, there arife in the mixture new and unlook'd-for confiftences and other qualities or accidents. And tho' it may fometimes happen, that thefe new qualities fhall prove advantageous, yet this may well be look'd upon but as a lucky chance; and it may ftill be juftly fear'd, that, ordinarily, fuch accidental qualities of a medicine will prove to be either worse than were expected, or at leaft different from what was defign'd, and confequently lefs fit for the phyficians or the artifts purpose.

made in a dar

1. Octob. 11. About ten in the morning, the weather being fun-fhiny, PHYSICS. we took feveral forts of ftain'd paper, fome of one colour, and fome of another, and in a darkned room, whofe window look'd fouthward, we with Experiments them caft the beams that enter'd at a hole about three inches and a half in ken'd room. diameter, upon a white wall that stood on one fide, about five foot distance from them. The white gave much the brightest reflection. The green, red, and blue being compared together, the red gave much the ftrongest reflection, and manifeftly threw its colour upon the wall; the green and blue were scarce difcernible by their colours, and feem'd to reflect an almoft equal light. The yellow, compared with the two laft, reflected fomewhat more light. The red and purple being compared together, the former manifeftly reflected much more light than the latter. The blue and purple compared together, the former feem'd to reflect fomewhat the more light, tho' the purple colour was moft vifible. A fheet of very well fleek'd marbled paper being apply'd as the others, did not caft any of its diftinct colours upon the wall, nor throw its light with an equal diffufion thereon; but fent the beams unftain'd and bright to particular parts thereof, as if its polish had given it the nature of a speculum. But comparing it with a fheet of white paper, we found the reflection of the latter to be much the stronger; this diffufing almost as much light to a confiderable extent, as the marble paper did to one part of the wall. The green and purple left us fomewhat in fufpence which reflected the moft light; only the purple feem'd to have fome little advantage over the green, which was dark in its kind.

2. Though a darken'd room be generally thought requifite to make the colour of one body appear by reflection from another that is not fuppofed to act as a speculum; yet I have often obferv'd, that when I wore waftcoats lined with filk that was very gloffy and vividly colour'd, but efpecially if red, I could in an enlighten'd room plainly difcern the colour upon the pure linen that came out at my fleeve; as if that fine white body were more of a mirror than colour'd and unpolifh'd bodies are usually fuppofed.

3. Holding ftain'd fheets of paper, fometimes one, and fometimes another, before the hole of the window in the darken'd room, betwixt the fun and the eye, with the colour'd fides obverted to the fun, we found them fingly to be fomewhat transparent, and to appear of the fame colour as before, only a little alter'd by the great light they were placed in: but applying two of them one over another to the hole, the colours were compounded as follows: The blue and yellow fcarce exhibited any thing but a darker yellow, which we afcribed to the coarseness of the blue paper, and its darkness in its kind. For applying the blue parts of the marbled paper with the yellow paper after the fame manner, they exhibited a good green. The yellow and red look'd upon together, gave us but a dark red, a little inclining to an orange-colour. The purple and red view'd together, appear'd more deeply fcarlet. The purple and yellow made an orange. The green and red made a dark orange-tawny. The

green

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