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fpar, (a fubfpecies of heavy spar, or nativefulphat of barytes) winch he had procuredfrom Monte Paterno in the neighbourhood ofthe city; and obferved that whenever this fub-ftance thus prepared was placed in a dark room,after having been expofed to the fun, it conti-nued to emit faint rays of light for fome hoursafterwards. In confequence of this intereftingdifcovery the Bolognian fpar came into confi-derable demand among' natural philofophers,and the curious in general, fo that the beftmethod of preparing it became an objeff ofeven fome pecuniary importance. The familyof Zagoni were the moft fuccefsful in this pur-fuit, and in confequence furnifhed large quanti-ties of Bolognian pnofphorus to all parts of Eu-rope till the fubfequent difcovery of more pow-erful phofphori put an end to their monopoly.The particular procefs employed by the Zagonisis not known, but we learn from Kircher thatif the mineral is finely pulverized and thenbeaten up into a pafte with white of egg orlinieed oil, and calcined in the open fire, it willafter expofure for a minute to the light exhibitits phofphorefcent quality. Many years after-wards Marggraaf in'analyfing other varieties offulphated barytes found that they were all ca-pable of being made into phofphori by form-ing them, when pulverized, into thin cakeswith gum tragacanth or other mucilage, andthen carefully calcining them at a red heat.Some management however is requifite in con-ducing the calcination that it may be neithertoo much nor too little, by either of whichfaults the luminous quality is very materiallyinjured.

In the year 1677, or nearly half a centuryafter the difcovery of the Bolognian phofpho-rus, G. A. Baldwin, a native of Mifnia, ob-ferved that if nitrat of lime was evaporated todrynefs and then formed into a compaft mafsby fufion at a red heat, it would exhibit thefame property of imbibing and emitting light asthe former only iomewhat inferior in degree;hence this preparation obtained the name ofBaldwin’s phofphorus.

No other difcovery of much moment wasmade on this fubjeC till the year 1730, whenM. du fay, fo celebrated for his eleCrical re-earches, turned his attention that way. He° erves that all earthy fubftances fufceptible ofca cmation either by mere fire or when affiftedy e previous aCion of nitrous acid, poflefledt e property of becoming more orlefs luminousw en a cured and expofed for a fhort time to

Aa. Bologn. 1744—1747.

the light. Thofe that exhibited this quality "inthe greateft perfeCion were found to be lime-,Hone and many other kinds of carbonated lime,gypfum, and particularly the topaz ; fome dia-monds were aifo obferved to be luminous byfimple expofure to the fun’s rays without beingprevioufly ignited; but flint, fand, jafper, agate,and rock-cry Hal, were found to be incapable ofbecoming phofphorefcent.

Shortly after thefe interefting difcoveries ofM. du Fay the fubjeft was taken up by Beca-ria a , who greatly enlarged the lift of phofpho-refcent fubftances and found tbat a vaft varietyof bodies were convertible into phofphori bythe mere light of the fun; this he obferved tobe particularly the cafe with regard to the dif-ferent varieties of carbonat and fulphat of lime,organic animal remains, and geodes lined withminute cryftals of quartz; moft compoundfalts when clear and cryftallized, particularlyGlauber’s fait, nitre, and borax, were alfo foundto be phofphorescent; of vegetable fubftances,all the farinaceous and oily feeds, all the gumsand feveral of the refins, the white woods, andvegetable fibre either in the form of paper orlinen, alfo ftarch, and loaf fugar, proved to begood phofphori after being made thoroughlydry and expofed to the diredt rays of the fun;fundry animal matters by a fimilar treatmentwere alfo converted into good phofphori, par-ticularly bone either frefh or calcined, fmew,glue, hair, horn, hoof, feathers, and fbells offilh. He alfo difcovered that this propertymight be communicated to rock cryftal andfome of the gems by rubbing them againfteach other fo as to roughen their furface, andthen placing them for fome minutes in the fo-cus of a lens by which the rays of light wereconcentrated upon' them at the fame time thatthey were alfo moderately heated.

In the year 1768, Mr. Canton 6 contributedfome important facts relative to folar phofphori,and communicated a method of preparing avery powerful one, which after the inventor isufually called Canton's phofphorus. It is thusmade. Calcine oyfter {hells in the open firefor half an hour, then feledt the whiteft andlargeft pieces and mix them with flowers offulphur in the proportion of one part of thelatter to three parts of the former, pack thewhole clofely into a crucible, lute on a cover,and heat it pretty ftrongly for one hour; whenthe crucible has again become quite cold turnout its contents, and felect the whiteft pieces forufe.

‘ Phil. Tranf, lriii, p. 337.

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