grinding verdigreafe with fal-armoniac and fome other faline ingredients, PHYSICS and fuffering them to lie for a good while together in a dunghill; for we fuppofed, that the change of colour wrought in the verdigreafe by this way of preparation, muft proceed from the action of certain volatile and alkaline falts, abounding in fome of the mixed concretes, and brought to make a further diffolution of the copper contained in the verdigreafe; and therefore conjectured, that if both the verdigreafe, and fuch falts, were diffolved in fair water, the fmall parts of both being therein more fubdivided, and fet at liberty, would have better accefs to each other, and thence incorporate much the fooner. And, accordingly, we found, that The production if, upon a ftrong folution of good French verdigreafe, we poured a juft of a blue colour. quantity of oil of tartar, and fhook them well together, a notable change of colour immediately fucceeded; the mixture growing thick, and not tranfparent; but if you ftay till the groffer part be precipitated, and fettled at the bottom, you may obtain a clear liquor of an exceeding delightful colour. You must drop in a competent quantity of oil of tartar, otherwise the colour will not be fo deep and rich; but if, instead of this oil, you employ a clear lixivium of pot-afhes, you may have an azure, fomewhat lighter or paler than the former. And if, inftead of eitherof thefe liquors, you make use of spirit of urine, or of hart's-horn, you will, according to the quantity and quality of the fpirit poured in, obtain fome further variety of blue liquors; and, by the help of this urinous fpirit, we have made a furprizing blue liquor. But thefe azure-coloured liquors fhould be freed from the fubfiding matter, which the falts of tartar, or urine, precipitate out of them, rather by being decanted, than by filtration; for, in the latter method, we have fometimes found the colour of them very much impaired. 23. That rofes, held over the fume of fulphur, may quickly be thereby of a red deprived of their colour, and have as much of their leaves, as the fume works upon, turned pale, we have already hinted; and it is a known experiment. But it may feem ftrange to one who has never confidered the compound nature of brimftone, that tho' the fume of it, as we enfue. Whilft this ebullition continues, pour the mixture out of one veffel into another, and afterwards let it reft. Then run the liquor thro' a linen, and let the pigment remain in the ftrainer; and when 'tis thus freed from its moisture, put it, by means of a wooden spatula, into a small new pot; pour upon it two or three ounces of spirit of falt, and there will immediately arife a moft beautiful blue. Let the matter be well stirr'd, and fet to reft for a night; and afterwards thoroughly edulcorate it with repeated affufions of rain-water; allowing a competent time for the precipitate to fubfide. Thus, at length, it will become exVOL. II. quifitely blue. Laftly, let it drain upon L have PHYSICS. have faid, whitens the leaves of rofes, yet the oil of fulphur per campanam, powerfully heightens the tincture of red rofes, and makes it more red and vivid; as we have eafily try'd, by putting fome red rofe-leaves, that having been long dry'd, had loft much of their colour, into a vial of fair water for a while after the affusion of a convenient quantity of the oil, both the leaves themselves, and the water they were fteep'd in, discover'd a very fresh and lovely red colour. Singe What quantity 24. It may ferve to illuftrate not only the doctrine of pigments, and of of limpid liquor colours, but many other parts of mechanical philofophy, as odors, and pigment may other qualities are explain'd by the affiftance of bodies extremely minute, to examine to how much of a colourless liquor, a very small parcel of a pigment may impart a difcernible colour. And tho' fcarce any thing of exactnefs can be expected from fuch trials, yet I prefum'd I fhou'd hence be able to fhew a much further fubdivifion of the parts of matter into visible particles, than feems hitherto taken notice of, or imagin'd. colours of many ductions The moft promifing bodies, for fuch a purpose, might feem to be metals, efpecially gold, because of the multitude and minutenefs of its parts, which might be argued from the great clofeness of its texture. But tho' we try'd a folution of gold, made in Aqua regia firft, and then in fair water, yet because we were to determine the pigment we employ'd, not by bulk, but weight; and because alfo the colour of gold is but weak, in comparifon of that of cochineal, we rather chofe this to make our experiments with. But, from a number of thefe, it may fuffice to select one which was carefully made in veffels conveniently fhap'd; to which I fhall only premife, that the cochineal will be better diffolv'd, and have its colour far more heighten'd by fpirit of urine, than by common water, or even rectified fpirit of wine. One grain of cochineal, diffolved in a confiderable quantity of spirit of urine, and then further diluted by degrees with fair water, imparted a difcernible colour to fix glaffes of water, each containing forty-three ounces and a half; which amounts to above one hundred twenty-five thousand times its weight. Acid, alkaline,. 25. It may afford a confiderable hint towards improving the art of dyand urinous ing, to know what change of colours are producible by the three feSalts, change the veral forts of falts we have mention'd, in the juices, decoctions, infufions, vegetable pro and the more foluble parts of vegetables. The blue liquors lately made ufe of in our experiments, are far from being the only vegetable fubftances upon which acid, urinous, and alkaline falts, have the like operations to thofe above recited. Ripe privet-berries, for inftance, being crush'd upon white paper, tho' they ftain it with a purplish colour, yet if we let fall on one part of it, two or three drops of fpirit of falt, and on the other, fome ftrong folution of pot-afhes, the former liquor immediately turns that part of the thick juice, or pulp, on which it fell, into a lovely red; and the latter changes the part whereon it falls, into a delightful green. This experiment is, perhaps, very extenfive, and ferviceable to thofe who wou'd know how dying ftuffs may be wrought upon by faline liquors, For I have found it to fucceed in fo many various berries, flowers, bloffoms, and other finer parts parts of vegetables, that my memory will not ferve me to enumerate them; PHYSICS. and it is furprizing to fee, by what differently colour'd flowers or bloffoms; for example, paper being ftain'd, may, by an acid fpirit, be immediately turn'd red, and by any alkali, or urinous fpirit, green; fo that even the bruis'd bloffoms of Mezereon, gather'd in frofty weather, and those of peafe crush'd upon white paper, how remote foever their colours are from green, wou'd in a moment pafs into a deep degree of that colour, upon the touch of an alkaline liquor. And either of these new pigments may, by a fufficient affufion of a contrary liquor, be prefently chang'd from red to green, and from green to red; which obfervation holds alfo in fyrup of violets, the juice of blue-bottles, &c. 26. There are, however, fome cases wherein these experiments will not uniformly fucceed. And firft, I try'd the operation of acid falts upon fuch vegetable fubftances as are in their own nature red; as fyrup of clovejuly-flowers, the clear exprefs'd juice of buckthorn-berries, red-rofes,infufion of brazil, and many others; on fome of which, fpirit of falt either made no confiderable change, or only alter'd the colour from a darker to a lighter red. And as to the operation of the other forts of falts, upon thefe red fubftances, I found it not very uniform; fome red or reddish infufions, as of rofes, being thereby turn'd into a dirty colour, inclining to green. Nor was the fyrup of clove-july-flowers turn'd by the folution of pot-afhes, to a much better, tho' a fomewhat greener colour. Another fort of red infufion was by an alkali not turn'd into a green, but advanc'd to a crimfon; tho' there were other kinds of them, particularly the juice of buckthorn-berries, that readily pafs'd into a lovely green. 27. Among other vegetables, which feem'd likely to afford exceptions to the general obfervation about the different changes of colours, produced by acid and fulphureous falts, we made trial upon the flowers of jeffemin; they being both white, as to colour, and esteem'd of a more oily nature than other flowers. Taking, therefore, only the white parts of the flowers, and rubbing them fomewhat hard with my finger, upon a piece of clean paper, it appear'd very little difcolour'd thereby; nor had fpirit of falt, wherewith I moiften'd one part of it, any confiderable operation thereon: tho' fpirit of urine, and, particularly, a ftrong alkaline folution, immediately turn'd the paper, tho' it had remain'd almoft colourlefs, of a deep greenish yellow; which experiment I feveral times repeated with the like fuccefs. But a great degree of unctuoufnefs feems unneceffary to the production of these effects; for when we try'd the experiment with the leaves of those pure white flowers that appear about the end of winter, and are commonly call'd fnow-drops, the event was much the fame with the last mention'd. 28. Another fort of inftances, to fhew how much the changes of colours effected by falts, depend upon the particular texture of the colour'd bodies, we have from feveral yellow flowers, and other vegetables, as marygold-leaves, primrofes, fresh madder, &c. For thefe being rubb'd white paper, till they imbued it with their colour, I cou'd not find, upon PHYSICS. by the addition of alkaline liquors, or of an urinous fpirit, that they would turn either green or red; even the fpirit of falt would not confiderably alter their colour, only dilute it a little: tho', in fome early primrofes, it deftroy'd the greatest part of the colour, and made the paper almost white again. Madder, alfo, afforded fomething peculiar; for having gather'd fome roots of it, whilft its yellow juice was fresh exprefs'd upon white paper, an alkaline folution being dropp'd upon it, turn'd it neither green nor white, but red; and the bruis'd madder it felf, drench'd with the like alkaline folution, exchang'd its yellownefs for a redness. 29. It may be of ufe, towards difcovering the nature of the changes which the alimental juices undergo in different vegetables, in their different degrees of maturity, to obferve what operation acid, urinous, and alkaline falts will have upon thofe juices. To fhew my meaning by an example, I took from the fame clufter one black-berry full ripe, and another that had not yet out-grown its redness; and rubbing a piece of white paper with the former, I obferved, that the juice adhering to it, was of a dark reddish colour, full of little black fpecks; and that this juice, by a drop of a ftrong lixivium, would immediately turn into a deep greenish colour; by as much urinous fpirit, into a colour near allied to the former, tho' fainter; and by a drop of fpirit of falt, into a fine light red: but the red berry, rubbed in like manner upon paper, left on it a red colour, which was very little altered by the fame acid fpirit; and from the urinous and lixiviate falts, received changes of colour, different from those produced in the dark juice of the ripe black-berry. I remember alfo, that tho' the infufion of damask rofes would be heighten'd by acid fpirits, to an intense degree of redness, and, by lixiviate falts, be brought to a darkish green; yet putting a rofe, whofe leaves were perfectly yellow, in a folution of falt of tartar, it afforded a green bluish tincture; but, by means of an acid liquor, I could not obtain a red one; the faline fpirit I employ'd, only a little diluting the yellowness of the leaves. And if I were in the islands of Banda, where cloves fo greatly profper, I fhould try what operation our three differing kinds of falts would have upon the juice of this fpice; which eminent authors inform us is at firft white, afterwards green, and then reddish, before 'tis beaten off the tree; after which, being dry'd, it grows blackifh, as we fee it. And one of the latest botanic writers informs us, that the flower grows upon the top of the clove itself, confifting of fmall leaves, like a cherry blossom, but of an excellent blue. 'Tis very proper to take notice of the particular feafons wherein the vegetables, defigned for the nicer experiments, are gathered. That diligent botanift, Mr. Parkinfon, tells us, that " of buckthorn-berries are made three "feveral forts of colours; being gathered green, and kept dry, they are call'd fap-berries; which being fteep'd in alum-water, give a fair yellow colour, ufed by painters, bock-binders, and leather-dreffers, who alfo make a green colour, called fap-green, taken from the berries, when they are black; that being bruifed, and put into a brafs kettle, and 66 "there "there fuffered to remain for three or four days, with fome beaten alum PHYSICS. put to them, they are afterwards preffed, and the liquor ufually put into bladders, and hung up till it be dry: this, he fays, is afterwards diffolved in water, or wine, but canary is the beit to preferve the colour from ftarving. The third is a purplish colour, made of the berries, fuffered to grow upon the bushes, till the middle, or end of November, when they are ready to fall of themfelves." And I try'd, with success, to make fuch a kind of pigment as painters call fap-green, by a way not unlike that here delivered by our author. Much after the fame manner, alfo, they make fap-green in the colour-fhops. Particularly a 30. Many bodies, digefted in well-clofed veffels, change their colour in Changes of colour tract of time, as rectify'd fpirit of hart's-horn; and the fame is evident in by digestion, &c. the precipitations of amalgams of gold and mercury, without addition; rednes where, by the continuance of a due heat, the filver-coloured amalgam is reduced into a fhining red powder. And many other inftances of the like kind, might be produced. Now, in thefe operations, there appears no reason why we fhould attribute the new colours to the action of a new fubftantial form; nor to any increafe, or decrease of the falt, fulphur, or mercury of the matter that acquires them. For the veffels are clofed, and thefe principles, according to the chymifts, are ingenerable, and incorruptible. So that the effect feems to proceed from the heat, agitating and difcompofing the corpufcles of the body expofed to it; which, in procefs of time, fo changes its texture, that the tranfpofed parts modify the incident light, otherwife than when the matter appeared of another colour. 31. Among the feveral changes of colour which bodies acquire, or difclofe, by digeftion, it is very remarkable, that chymifts find a redness, rather than any other colour, in moft of the tinctures they draw; and even in the more grofs folutions they make, of almoft all concretes that abound either with mineral or vegetable fulphur; tho' the menftruum employ'd about thefe folutions, or tinctures, be never fo limpid. This we have obferved in abundance of tinctures, drawn with fpirit of wine from jalap, guaiacum, and many other vegetables; and not only in the folutions of amber, benjamin, &c. made with the fame menftruum; but alfo in several mineral tinctures. And, not to urge that familiar inftance of the ruby of fulphur, as chymifts call the folution of flowers of brimftone, made with the fpirit of turpentine; nor to take notice of other more known examples of the aptiefs of chymical oils to produce a red colour with the fulphur they extract or diffolve; 'tis remarkable, that both acid and alkaline falts, tho', in most other cafes, of contrary operations, will, with many bodies that abound in fulphureous, or oily parts, produce a red as is manifeft in the vulgar inftances of the tinctures, or folutions of fulphur, made with lixiviums, either of calcined tartar, or pot-afhes, and other obvious examples; and in that the true glafs of antimony, extracted with fome acid fpirits, yields a red tincture. And a certain acid liquor will, in a moment, turn oil of turpentine into a deep red. |