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iron-'grate a confiderable time. The other experiment Is, the application of the paper to a plate of warm brafs; from which, when in the dark, you might very eafily, by its be- ing lefs luminous, diftinguifh the margin of the paper that had not been warmed by the brafs. The fore mentioned au- thor takes notice alfo of thofe phofphori which become fo by the affiftance of fire ; but the fire here fpoken of is not great enough to diffolve their conftituent parts, but only fuch as may affect the external parts of their texture, and that but gently ; fo that the procefs here mentioned is only drying or roafting. For it is not the watry or the (aline parts in bodies which are torrified ; but the oleaginous, wherewith many ve- getables, and moft animals abound. The white fJcfh of ani- mals, fuch as that of chickens, becomes a pbofpborus by roaft- in», as well as the tendons ; and whatever parts of animals become glutinous by boiling, fuch as carpenters glue, ifing- glafs, &£• to thefe may be added cheefe. Bones, though they imbibe light without any preparation, have that pro- perty in a much greater degree when burnt, and their lumi- nous appearance is much more lively. But roafting has not this effect upon feathers, hoofs, horns, or whites of eggs. The fame operation which produces feveral pbofph.ri from the animal kingdom, gives alfo feveral from the vegetable. Thus, by gently toafting gums, as myrrh, gum tragacanth, and others, they appear luminous tho' different in degrees ; and this light is clear in proportion to the gentle evaporation of their aqueous parts. By this treatment nuts of every kind, pulfe, corn, coffee-berries, meal, bread, and wafers, alfo become phofphori. Turpentine, amber, and fome refins, require more fire before they imbibe light ; fo that you muff diveft them of their acid, and their light etherial oil, to make them ap- pear luminous. But here great care muft be taken that they boil no longer than from being white they turn yellow ; for if you proceed longer, your labour is loft. Thofe phofphori produced by torrefaction, foon lofe their power, which, per- haps, neither time nor a thorough diffolution of their parts can deprive the natural ones of. In genera!, as long as the phtfphm gained by torrefaction, preferve their power, their light is more fharp and ftriking, but the natural more weak. Thofe that are gained by calcination, and Baldwin's pbofpbo- rus, feem to polTefs both the ftriking light of thofe gained by torrefaction, and the weaker light of the natural phof- phori : the latt they preferve a long time, but the former is loft by degrees much fooner. The well calcined allies of plants, or rather their terreftrial parts remaining after the fo- lution of their fixed falts by wafhing, and neutral falts, con- tinue phofphori after many years : fo that, as far as we can judge, the luminating power which is gained by calcination, tho' not fo intenfe, continues perpetual ; whereas that gained by torrefaction always decreafes, and in a very little while is no longer viable. Some even by this method, continue to imbibe light much longer than others. Gum arabic, which continues longeft, lafts fix days ; bread not one, and coffee only a few minutes. However, at any time, by a frcfti torrefaction, you may recover thefe languid phofphori ; in which property they have great likenefs to the Bolonian ftone, and other phofphori prepared by art. The phofphori gained by torrefaction, as well as that of Bolonia, will not imbibe light while they are warm ; and this laft does not appear fo lumi- nous when firft prepared, as when it has been fo for fometime. The natural phofphori do not differ only in the before-men- tioned particulars, but alfo in the colour of the light vtfelf. The light of the natural generally appears either perfectly bright, or fomewhat inclining to yellow; the artificial pro- duces a red, and fometimes a brown light; but there are fome exceptions to both thefe rules. From thefe different appear- ances it may be conjectured, that there are two fons of fire arifing from different principles ; viz. that in torrified fub- ftances from a fulphureous, and that of the natural from a terreftrial principle. In obferving a piece of lapis tutise, that vras rough and unequal on its convex fide, but fmooth and fomewhat polifhed on the concave, Beccari, to his great fur- prife found, that the rough fide was luminous, and the fmooth one not : being very defirous of inveftigating the caufe of this appearance, he remembered that fome polifhed marbles did not imbibe light, or very little, and that at their edges ; but having loft their polifh, they did admit and retain it. He therefore conjectures, that bodies, according to the dif- pofition of their furfdces for the reflection of the light, either fuffer or prevent its entrance into them. If this pofition hold good in the reflection, Why ihould it not with regard to the refraction ? The fame author produces two experiments, which he apprehends not foreign to the prefent purpofe. Ex- pofing a jrlais- bottle full of well water to the light, and, as loon as poflib.'e, obferving it in the dark, it was found to have imbibed no light; upon pouring into it fome oil of tartar, it became turbid and whitifh, from the well-water being ufually impregnated with calcarious matter. Upon ob- ferving it then in the dark, after having been expofed as be- fore, it retained enough of a pale light to diftinguifh the fhape of the bottle, in a bottle of rain water he diflblved fome talc; which ftone, by rubbing, will diflblve in water as falts do, without rendering it opaque ; to this folution he added oil of tartar, and this mixture was luminous as the
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preceding. He therefore concludes, that fo Yang as e'arthV corpufcles are very final!, feparate, and agreeing in their fur- faces With the water in which they float, they readily tranf" mit the light they receive; for which reafon 'tis impoffible they ihould retain light enough to appear luminous in the dark. But by the affufion of the fahne principle, the earthy corpufcles unite with the water and fait ;, and from the union of thefe principles the mixture grows thick, whereby the ready tranfmiffion of the light is prevented; fo that if this mixture is without colour, or any thing metallic, the li»ht will be flopped long enough to be vifible in the dark. But jf, mftead of oil of tartar, you add fugarof lead, the mix- ture will be turbid, but retain no light. In thefe two ex- periments the water becomes a phfhorus. Gems, cryftal, and glafs, whether whole, or powdered ever fo fine, retain no light ; fo that neither their tranfparency nor whitenefs con- tribute to their becoming luminous in the dark. Of feveral diamonds in all appearance perfectly the fame, fome were very luminous, others not at all. Of many opaque fub- ftances, whether rough, polifhed, or finely powdered, fome were luminous, others not : fo that it appears that not only the external, but the internal texture of bodies alfo, may con- duce fometimes to their being luminous.
Almoft all bodies, by a proper treatment, have that power of fhining in the dark, which, at firft, was fuppofed to be the property of one, and afterward only of a few. How this is brought about is not eafy to folve. If we fuppofe with fome, that the light from a luminous body, enters and abides in the phofphori, we fhall find fomewhat new to admire in light it- felf It is no new opinion, that this fluid confifts of very fine particles, which are continually darted forth from a lu- minous body in all directions, with a very great velocity : but it has by no body been laid down hitherto, that thefe particles are not diffolved by the violence of their agitation* not difperfed, nor immediately ceafe to exift ; but fubfift ftill, and adhere to what bodies come in their way, as heat does. If therefore the particles of light are not diffolved as foon as they are emitted from a radiant body, but continue fome time what elfe is required but that we allow its atmofphere to every lucid appearance? If the pbofobori fhine with a bor- rowed light, but not with their own, and that only when put in motion, and fired by the rays of a fhining body, which fome experiments feem to confirm, then other new doctrines will arife. There muft be then a hidden, a fecret principle in bodies, to be lighted up by this moft fubtle fire. There will be in the univerfe a certain perpetual fire from thefe phofphori; the matter of which, tho' conftantly diflipated by- burning, does not wafte enough to be obvious to our fenfes See Phil, Tranf. N° 478. Phosphorus of urine. The fuccefsful method of making this famous fubftance is this : evaporate any quantity of frefh urine over a gentle fire, to a black and almoft dry fubftance ; ther^ with two pounds thereof, thoroughly mix twice its quantity of fine fand ; put the mixture into a ftrong coated retort of ftone, and having poured a quart or two of water into a large receiver with a long neck, join it to the retort, and work it in a naked fire: let the heat be fmall for the two firft hours, and then increafe it gradually to its utmoft violence, and con- tinue thus for three or four hours ; at the expiration of which time there will pafs into the receiver a little phlegm and vola- tile fait, much black foetid oil, and laftly, the matter of the pbofpborus, in form of white clouds ; which will either ftick to the fides of the receiver, like a fine yellow fkin, or elfe fall to the bottom, in form of a fmall fand. Now let the fire go out, but take not away the receiver before it is cold, for fear of fetting the pbofpborus on fire by admitting the air. Take out the matter of the pbofpborus-, and put it into a little tin ingot mould, along with water; heat the mould to make the matter all run into a mafs, then add cold water, till it is con- gealed into a folid mafs like bees- wax ; cut this into long flen- der pieces, which put into a phial, and fill it up with water, and then cork it clofe. Shaw's Lect. p. 403. This pbofpborus is nothing but the animal fulphur. Now all animals, on which experiments have been made, are found to contain more or lefs of the phofpboreal principles ; fome infects conftantly fhine, or emit light, in the open air; ma- ny forts of fifli are luminous, if expofed to the air a fhort time; nay, even the bubbles of the fea water appear like fire in the dark : fome quadrupeds have been obferved to emit light on very flight friction of their hair, as the necks of horfes, the backs of cats, and the like ; and there are many inftances in our own fpecies of many parts of the bo- dy appearing luminous, and even of the exhalations from it adhering to the cloaths, caufing them to fhine likewife. "We have feveral curious obfervations relating to tin's fubject in the Phil. Tranf. N y 47 D - P- 444s 445) 45^ 457, & c - Upon this principle of pbofphrus exifting in animals, fome attempt to explain the caufe of thofe accidental accenfions or burnings which have happened to fome of the human fpe- cies, as that of the lady at Cefena in Italy, the carpenter in Hampfhire, and the woman lately at Ipfwich. It feems moft probable, that they were all fet on fire by lightening. It may be faid, many are ftruck by lightening, but not fet on fire. But it is to be remarked, that the lady at Cefena had charged
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