PHYSICS. and fuch bodies chymically prepared, as belong neither to the animal kingdom, nor to the tribe of alkalies, have their new nature fuccefsfully examined. But to change the colour of this fyrup, it requires that the body be more strong of the acid or other falt predominant in it, than is neceffary to work upon the tincture of Lignum Nephriticum: and tho' the actions of these contrary falts will destroy each other, yet neither of them will reftore the fyrup to its native blue, as in the nephritic tincture; but each of them changes it into the colour which itself affects. 21. By dropping on the fresh juice of blue-bottles, or the Cyanus vulgaris minor, a little fpirit of falt, it immediately turn'd to a red. And if instead of the acid fpirit, I mix'd with it a little ftrong folution of an alkaline falt, it prefently difclofed a lovely green; the fame changes being, by thofe different forts of faline liquors, producible in this juice, as in fyrup of violets. And finding this blue juice, when fresh, to be capable of serving for an ink of that colour; I attempted, by moistening one part of a piece of white paper with the fpirit of falt, and another with fome alkaline or volatile liquor, to draw a line on the paper after it was dry, that should appear partly blue, partly red, and partly green: but the latter part of the experiment did not fucceed well, tho' the blue and red were confpicuous enough to furprize those who were unacquainted with the trick. But left it should be thought that volatile or alkaline falts change blue into green rather upon the fcore of the eafy tranfition of the former colour into the latter, than upon account of the texture, wherein most vegetables, that afford a blue, seem to be allied; I fhall add, that having diffolv'd blue vitriol in fair water, and put a lixiviate liquor and an urinous falt to distinct parcels of it, each of them turn'd the liquor not green, but of a deep yellowish colour, almoft like that of yellow oker; which colour, the corpufcles thereby precipitated, retain'd. 22. The hint of the following experiment was afforded us by the pratice of fome Italian painters, who counterfeit ultra-marine azure by The Pruffian blue is allow'd to excel the ultra-marine. And the preparation of it being very curious and ufeful, we fhall here give an extract of that receipt for it which was lately communicated to the Royal Society by Dr. Woodward, as fent him from Germany. Take of crude nitre and crude tartar, each four ounces; powder them fine, mix them together; and after decrepitation, there will remain four ounces of a falt of tartar: whilt this is hot, pulverize it, and add thereto four ounces of well-dry'd ox-blood, in fine powder. Calcine the whole in a cover'd crucible, whereof it may fill two thirds. After this operation, lightly grind the matter in a mortar, and put it hot into * grinding Strain four pints of boiling water; and let it 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 verdigrease; and therefore conjectured, that if both the verdigrease, and such falts, were diffolved in fair water, the fmall parts of both being therein more subdivided and fet at liberty, would have better access to each other, and thence incorporate much the fooner. And, accordingly, we found, that The production of if, upon a strong solution of good French verdigreafe, we poured a juft a blue coquantity of oil of tartar, and shook them well together, a notable change of colour immediately fucceeded; the mixture growing thick, and not transparent; 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, otherwife 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, instead of either of thefe liquors, you make use of spirit of urine, or of hart's-horn, you will, according to the quantity and quality of the spirit poured in, obtain fome further variety of blue liquors; and, by the help of this urinous spirit, we have made a furprizing blue liquor. But these 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 brimstone, that though the fume of it, as we enfue. Whilft this ebullition continues, pour the mixture out of one vessel 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 fpatula, into a fmall new pot; pour upon it two or three ounces of fpirit 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 some red rose-leaves, that having been long dry'd, had loft much of their colour, into a vial of fair water for a while after the affufion of a convenient quantity of the oil, both the leaves themselves, and the water they were steep'd in, difcover'd a very fresh and lovely red colour. What quantity of limpid liquor a pigment may tinge. 24. It may serve to illuftrate not only the doctrine of pigments, and of colours, but many other parts of mechanical philofophy, as odors, and 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 exactness 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. The moft promifing bodies, for fuch a purpose, might feem to be metals, especially gold, because of the multitude and minutenefs of its parts, which might be argued from the great clofenefs of its texture. But tho' we try'd a folution of gold, made in Aqua regia first, 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 comparison 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 fpirit 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. 25 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 feveral Salts, change forts of falts we have mention'd, in the juices, decoctions, infufions, and the colours of many vegetable the more foluble parts of vegetables. The blue liquors lately made ufe productions. of in our experiments, are far from being the only vegetable substances upon which acid, urinous, and alkaline falts, have the like operations to those above recited. Ripe privet-berries, for inftance, being crufh'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 extensive, and ferviceable to those who wou'd know how dying stuffs may be wrought upon by faline liquors. For I have found it to fucceed in fo many various berries, Howers, bloffoms, and other finer 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 thofe of pease 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 thefe new pigments may, by a fufficient affusion 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 first, 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 these red fubftances, I found it not very uniform; fome red or reddish infusions, as of roses, 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 crimson; 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 efteem'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' spirit 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 thefe 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 laft 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 upon white paper, till they imbued it with their colour, I cou'd not find, PHYSICS. by the addition of alkaline liquors, or of an urinous fpirit, that they would turn either green or red; even the spirit of falt would not confiderably alter their colour, only dilute it a little: tho', in fome early primroses, it deftroy'd the greatest part of the colour, and made the paper almoft white again. Madder, alfo, afforded something peculiar; for having gather'd fome roots of it, whilft its yellow juice was fresh exprefs'd upon whitepaper, an alkaline folution being dropp'd upon it, turn'd it neither green nor white, but red; and the bruis'd madder it self, drench'd with the like alkaline folution, exchang'd its yellowness 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 cluster 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 specks; and that this juice, by a drop of a strong lixivium, would immediately turn into a deep greenish colour; by as much urinous spirit, into a colour near allied to the former, tho' fainter; and by a drop of spirit 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 though the infufion of damask roses 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 spirit 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 blackish, 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 bloffom, 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 botanist, Mr. Parkinson, 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 steep'd in alum-water, give a fair yellow "colour, used by painters, book-binders, and leather-dreffers, who also "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 |