Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/568

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.If verdlgreafc be boiled a cohfiderable time In white wax, it tinges marble, when rubbed hot upon it, to a beautiful green, little inferior to that of the coarfer emeralds, and the colour fpreads itfelf very equally, and penetrates to a third of an inch deep; if the marble be made too hot, the colour becomes that of the jade/owc Alkanet boiled in white wax gives a fiefh colour, which penetrates very deep ; and the roucou boiled in wax makes a permanent yellow,

■ which alfo finks very deep. The beft way of heating marble for this purpofe, is to lay the piece, intended to be ftained, upon a bed of fand, a fifth of an inch deep, upon an iron plate ; this is to be fet over the fire, and when of a proper degree of heat, the colour is to be applied. The juft de- gree can only be found by experience, and it varies indeed in almoft every colour; but in general,, the finer colours re- quire the marble to be of fuch a heat, that the hand can juft bear to be laid upon it, and the others require a fome- thing greater degree than this.

Black is, of all colours, the moft difficult to give in this manner to marble ; and perhaps indeed it is impoffible to give that colour in any degree of perfection, and that for this plain reafon, that all thefe colours only fill the inter-

■ ftices between the granules of the marble, thofe granules i themfelves remaining unaltered : thus, in the other colours,

the whitenefs of the granules is only a heigh tning to the . tinge, making it brighter, and a little paler ; but the white- nefs can never fail to appear diftinguifhably as fuch in black, and by that means deftroy that colour. Next to black, blue feems the moft difficult, of all the co- lours, .to give to marble. Mr. Du Fay, however, having found by Mr. Geoff roy's experiments, that oil of thyme, by long ftanding with fpirit of fa! armoniac, acquired a blue colour, tried this mixture, and found it fucceed very beau- tifully. But this is one of thofe colours which require the marble to have but a very fmall degree of heat, fince a greater would evaporate them before the colour had time to penetrate. The colours of the gums may be laid on when the marble is cold, and on heating it afterwards they will fink into it.

There is another very elegant fort of workmanfhip to be employed on marble, that is, the tracing figures in relief in it; and this is done much more eafily than might be ima- gined, there being nothing more required to it, than the • faving the parts which are to be left in relief, by covering them with a varnifh, and eating away the reft by means of an acid. For this purpofe let the defigned figures be traced in chalk upon the marble, and cover them with a bed of varnifh, made by diflblving a piece of common red fealing- wax in fpirit of wine j then pour on the marble a mixture of equal parts of fpirit of fait and diflilled vinegar, and this will eat down all the ground, and leave the figures ftanding, as if engraved with immenfe trouble. The adding the co- lours, before defcribed, to thefe marbles afterward, in a re- gular manner, will give them a furprifing beauty. Mem. Acad. Par. 1728.

EleElrhal attraction of Stones. Many Jiones have been ob- ferved by Dr. Lifter to have a fort of eleftrical attraction to vegetable refins.

This author obferves, that having placed fome foftils in a cabinet made of Barbadoes cedar, and examining them at fome diftance of time, he found them all covered with a li- quid refin like Venice turpentine. Many of t\\z Jiones were wrapt up in papers, yet thefe, as well as the reft, were co- vered with this refin ; though, upon the moft diligent fearch, there could not be found any exfudation on any part of the cabinet. The iron ores were moft of all covered with refin, all the kinds of the haematites being thick coated with it ; and among the aftroitse fome were thinly covered, and others perfectly free from it.

It was not owing to the texture and denfity of the Jiones, .that they either efcaped this, or had it, but thofe of the moft open grain, and thofe of the clofeft, were indifferently co- vered with it. It is certain from this Angular obfervation, that the whole body of the turpentine of the cedar wood was carried up into the air, and floating in it was again con- denfed, on the coming into contact with czrtzm Jlo?ies, tho' not with others.

There are feveral vegetable fubftances, which in this man- ner emit their whole body into the air : of the number of thefe is camphor ; but the Jlone, that will again condenfate this into camphor, is not known. Philofoph, Tranfacf N- no.

Formation of Stones. See Lithogenesia.

Medical Stones, a term ufed by fome to exprefs thofe parti- cular Jiones, which for their real or imaginary virtues have, at one time or other, been made ingredients in medicinal preparations.

The opinions of the antients, in regard to the virtues of gems and precious Jiones, were very whimfical ; they fup- pofed that they had certain fympathetic properties, and that the wearing them on the finger, or carrying them in the pocket, would cure difeafes, render the Gods propitious to their prayers, or fave them from thunder. Thefe have been defervedly laughed out of the world in our more enlightened

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times ; but it has remained a queftion, and does fo even to this time, whether or not fome of the gems have real medical virtues, naturally refulting from their parts, and conftituent matter. It appears from the prefent ftate of the gems, that they were once fluid bodies, or, at leaft, made up in part of fuch fubftances as were once fluid ; and as in this ftate they were capable of receiving metalline admixtures, it is poffible they may derive certain virtues from thofe admixtures ; and fome concurrent circumftances in that mixture mav have ex- alted the virtues of the bodies received, beyond what they could naturally and fingly have excited. The diaphaneiety, the external figure, and the internal ftrudture of gems, all argue ftrongly for their having once been in a fluid ftate ; and their colours, which feem to be evidently adventitious, and imparted either by fome coloured mineral juice, or fome tinged exhalation, could have fo deeply affected the denfe texture of thefe Jiones, as to pafs through all their parts in no other manner, than when that Jlone was in filutis principiis, or in a fluid ftate. There are fometimes found extraneous matters lodged in the bodies of the gems themfelves, which could only have been enveloped in them in this manner while they were foft ; and even in moft of them, the art of the chemift is able to difcover real particles of metals, which muft have been mixed in their fubftance at fuch a time, and to which they may very probably be indebted for real virtues. Rubies, when too fmall to be of value as gems, are in fome places, where they make a fort of fand in the rivers, worked to fome advantage as ores of gold. The amethyft evidently contains iron, and the emerald copper ; why fhould it then be fuppofed impoffible, that the virtues of thefe metals may be found in the gems Which contain themfelves, and that in fo pure and fine a ftate, as no chemical procefs can afford them in ? The weight of many of the coloured gems is much greater than could be expefled in Jiones of that hardnefs and confidence, and is plainly owing to the admixtures of the metalline particles of the various forts they contain. Mr. Boyle's opinion of the origin of the real virtues of the gems, is, that while the petrefcent matter was yet in a fluid ftate, the mineral matter was received into, and intimately mixed with it, fo as that the whole became but one Jlone ; and that the virtues are always fuch,. as may be derived from the impregnating metal or mineral, and are various in de- gree, according to the various ftates of the metal, and its quantity received into the compofition. If this fyftem holds good as to the gems, it will be much more naturally applicable to the femipellucid Jiones; many of which have gravities fo great, as plainly to denote the metalline or mineral matter that makes a part of them. The metalline fubftances, that may be feparated out of thefe Jiones, give great proof of the truth of this fyftem : thus the hasmatites contain a very large quantity of iron, and the lapis lazuli, and turquoifeyrW, contain very large quantities of copper ; and many of the jafpers hold no inconfiderable portion of the fame metal. Boyle of the Origin and Virtues of Gems.

Stone for building. Care muft be taken to dig Jlone at the proper feafon ; for thit Jlone which, taken out of the quarry at one time, would foon moulder away, will at another fea- fon endure the weather for many years, if not ages. Boyle's Works Abr. Vol.1, p. in.

Bolonian Stone. See Lapis Bononienjis.

Chalk Stones. See Chalk.

Chick Stone. See Cicerum lapis.

Copperas Stone. See Lapis atramentarius.

Eft Stones, See Eft.

Figured Stones. See Figured _/?m«.

Flejh Stone. See Sarcites.

Free Stone. See Free Jlone.

Gypfme Stone. See Gypsine.

Horn Stone. See Lapis corneas.

Moor Stone. See Moor.

Oil of Stones. See On of Jiones.

Shiad Stones, among the miners of Cornwall. See the article Shoad Jlo/ies.

Staining of Stones. See Staining.

Stone, in commerce. The ftone troy, in Scotland, contains iixteen pounds, the pound being two marks, or fixteen ounces. Tr. Praa. Geom. p. 153. See Pound.

Stone -inyfc, in agriculture, is a light lean foil, full of larger and fmaller maffes of rubble Jiones.

Thefe are to be tilled according to the condition in which they are found, for if they are graffy they fallow them pretty late ; but if they have no grafs upon them, they fold them in winter, when the fheep's dung, with the help of fome hay-feed, will furnifti them with grafs : or clfc, early in the fpnng they lay upon them old thatch or ftraw, or the ftrawy part of old dunghills, earth out of ditches, or the like, which will all, more or lefs, help forward a coat of grafs upon the land ; for it is a rule in regard to thefe lands, that they muft have a covering of grafs before they are fallowed, elfe they will yield but a poor crop. Plot's Oxfordfhire, p. 247. See Stony land, infra.

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