Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/604

 TAL

thing farther toward a folution of the Talc : Even after re- peated trials of this, the Talc is only changed to a fort of aft- colour, which is owing to the impurity of the earth contained in the fulphur. This is to be underftood of the pure and genuine Talc, fuch as that of Mufcovy, commonly called Oinglafs ; for the black and yellow kinds of Talc, after re peated calcinations, will be finally diflblv'd in concentrated aqua-regalis, or in very ftrong fpirit of fait, into a yellow li- quor refembling the folutions of gold. This colour, in the folution, has given fome perfons idle notions of its containing gold or folar fulphurs, as they exprefs themfelves ; but an ac- curate examination fhews, that this colour is only owing to fome attenuated particles of iron ; and upon evaporation of the folution, there remains a mere crocus martis. If frefh aqua regalis be continued to be poured on this yellow Talc, it will draw ftill more of a yellow tincture from it, till the remaining matter be perfectly white, retaining no remains of its golden appearance.

Common fire has very little efficacy upon Talc, it neither making it crepitate, nor melt, nor reducing it to the condi- tion of gypfnrn or lime : All the change it can make in it, is the rendering it in fine fomewhat more brittle, and in part deftroying its foliated ftru&ure. It fuffers no diminution all this time in weight, and is as bright and lucid, and as unctuous to the touch afterwards as before. Angelus Sala had Talc kept Forty days in a glafs-houfe fire, and at the end of that time took it out unaltered : But according to the expe- riments of Neuman and Hoffman, the folar fire, concen- trated by powerful burning-glaffes, melts this ftubborn fub- ftance into a greyifh kind of glafs. Thus we may eafily con- clude, that when Morhoff and the great Boyle talk of re- ducing Talc into a kind of gypfum in a common fire, in the fpace of an hour, they deceived themfelves, and ufed fome other fubftance which had the appearance of Talc, but was not fo ; fuch is the plated felenites, which cannot be diftin- guifhed from the pureft ifinglafs, till it is tried, by bending its feparated plates, thefe being not at all elaftic, as thofe of Talc are.

The action of falts rendered fluid by fire is much more power- ful upon Talc than any of thefe before-mentioned fubftances ; but to this purpofe the fire muff be very violent, the common fire of fufion producing nothing ; hence it », that authors in j

feneral have not found the effect of this procefs ; for they af- | rm that Talc, in a ftrong fire, mixed with three times its own quantity of a fufile fait, fuffers nothing, but renders the j fame appearances afterwards as before. Neuman alfo affirms, that he had ufed nitre, borax, and the corrofive falts in the | fame manner, without the lead fuccefs : But Mr. Pott | gives a different account of fuch proceffes, which he tried not with the common fire of fufion, but with the higheft degree he was able to give.

In his trials with this violent heat, Talc, fated with a folution of a cauftic alkali, run into a lax and fpungy mafs. Mixed with half its quantity of a purified alkaline fait, it run into an opake and blackifh mafs. Talc calcined in a common fur- nace, and then mixed with half irs weight of an alkali, melted and run into a hard and ftony mifs of a brownifh black, which was capable of the fine polifh of an agate ; and on repeating the fame experiment afterwards, the mafs produced by it was of the fame hardnefs and denfity, but perfectly white as ala- bafter ; the colour was in many other trials found to be in great meafure owing to the cleannefs of the crucible, and to its containing no ferrugineous or other metalline or mineral matter. Kunkell has before obferved, that Talc mixed with fait of tartar, and with fritt, and put into the fire, eafily runs into glafs with the fritt, without any greater degree of fire than what is always ufed on this occafion : But Mr. Pott obferves that Talc, with an equal quantity of hepar fulphuris, does not run into a compact mafs, but rifes in foam and fpume to the top of the crucible, and acquires a yellow colour, and the mixture afterwards fuffers the greateft fire that common Talc can bear, unhurt. Talc does not detonate with nitre, be- caufe it contains no fulphur, but they afterwards vitrify toge- ther in a violent fire ; and this has been before obferved in the German ephemerides. Talc, mixed with an equal portion of fixed arfenic, runs into a white hard mafs ; and with double its quantity of Glauber's fait, it does not diflblve, but only becomes a white friable mafs, yellowifh on the furface. Talc, with equal parts of borax, runs in a violent fire into a tranf- parent mafs, refembling the gem called the aqua marina ; and melted with different mixtures of borax, nitre, and arfe- nic, it runs into vitreous mailes, of many different degrees of colour.

Talc is ufed with great fuccefs in the diftillation of acid fpirits ; that of fait is always naturally impure, and can fcarce be rendered pure but by an admixture of a talcy earth in the re- tort.

The mixture of Talc with different kinds and quantities of glafs, may be fuccefsfully performed with a violent fire, but not with a fmaller degree : Thus three parts of Talc with one part of cryftalline glafs, make only a fpongy and friable mafs in a common fire ; but in a more violent one they become a firm and folid mafs of a brown colour. Minium, or glafs of lead, mixed in equal quantities with Talc, and fet in a

TAL

violent fire, run into a yellowifh glafs refembling the opake pieces of amber ; and two parts of minium to one of Talc, produce a clear and tranfparent yellow glafs, which is of a hardnefs capable of giving fire with fteel. The alkaline earths, mixed with Talc, produce a mafs fcarce verifiable by any fire : Hence appears the reafon why copels made of lime and Talc are fovery hard to vitrify. Minium added to thefe mixtures makes them combine into a firm mafs, but without perfect fufion ; but borax added to them melts them readily into a true glafs. The gypfous earths mixed with Talc, will not unite into a mafs in any degree of fire ; but if borax be added, the Talc readily melts. Thus two parts of Talc, two parts of that fpar or gypfous matter called glades maria?, or the com- mon plated (par, with one part of borax, run into a yellow mafs refembling a topaz.

The argillaceous earths do not vitrify with 7^/^ but they run into a mafs of great hardneis, which will give fire with fteel, and is very ferviceable to make crucibles of, tbefc veifels not fuffering the glafs of lead to run thro' them. Talc, joined with the verifiable itones, forms no remarkable body, but the mafs remains friable ; but from thefe maffes, by the addition of proper matters to render them fluid, great variety of elegant compounds may be made. Thus Talc mixed in equal quanti- ties with powder of flints, on adding to the whole a fourth part of cryftal glafs, the whole unites into an opake but folid white mafs. Alkali fait added in equal quantity to Talc and flint, gives a tranfparent yellow glafs ; and white fand, Talc, and a fixed alkali, in equal quantities, afford a green glafs; with other mixtures of this kind, in different quanrities, the re- femblances of many beautiful ftones are produced ; and what is very remarkable, fome grains of metalline matter are often found on the fui face of the maffes.

Caefalpinus, Aldrovand, and fome others affirm, that Talc melted with copper, or added to copper, while in fufion, gave it a white colour ; this being taken for granted, authors have hence agreed that Talc contains an arfenical earth. But ex- periment fhews this to have been a falfe ailertion, in regard to Talc ; and probably it only owes its origin to the cant language of fome of the alchemifts, who have called the flowers of zink, Talc; tho' thefe alone muff, render copper yellow, not white. Antimony and Talc, firft calcined with nitre, run in a violent fire into a fort of flint, which will give fire with, fteel. With regulus of antimony and the black flux, it runs into a black mafs j and with bifmuth it calcines into a grey powder. So little is there in the propofals of the chemifts for the metallization of Talc by antimony and bifmuth. Mem. del'Acad. de Berlin, Ann. 1746.

In what part of Mr. Boyle's works the learned author from whom the foregoing extract was taken, has found that Talc may be reduced by common fire to a gypfum in an hour, we know not ; but we find that Mr. Boyic feys, that the calcina- tion of Tale is fo very difficult, that eminent chemifts have looked upon calxcs otTalc as counterfeits. Works abr. vol. r.

p; l60.

Mr. Boyle mentions the extracting of gold from Talc, as hav- ing fometimes fucceeded. See Works abr. vol. 1. p. 160. but vide fupra.

The mountains in Hungary and Germany many of them abound in the Muicovy laic, not inferior to the Talc of that country from whence it has its name. The mountain of Cliffuro, which is a part of mount Hatmus, as alfo mount Pyijipe, ihine like filver in all parts both day and night, pro- vided there be any moon.

The Talc in thefe hills is the only occafion of this. There are alfo Talc rocks near Spittal in Upper Carinthia ; and many other hills are faid alfo to contain great quantities of it; but there is a fort of felenites fo very like this Talc, that people are eafily deceived by its appearance. This felenites fplits into flakes like the Talc, but they are brittle. Brown'?, Travels. Mexico Talc. There is a famous cave fome leagues from Mexico, on the north-weft fide of the city, beyond the lake, the top and fides of which are faid to be lined with leaf gold ; but that of fuch a kind, that the common methods of fluxing the ores have no effect upon it. The Spaniards, after many trials, have given it over, but are ftill perfuaded by the In- dians that it is gold, and that the famous Montezuma ob- tained a great part of his treafures from this cave. The leaves, as they are called, are no more than fpangles of the fize of a man's nail ; and the account we have of it in the Philofophi- cal Tranfaetions, and the various methods attempted in vain to reduce it to metal, abundantly prove that it is only a yellow Talc. Vid. Phil. Tranf. N°. 39. Mufcovy Talc, a kind of foliaceous body, well known by the Englifh name of ifinglafs. See the article Specularis Lapis. Pbilofopbic Talc, a name given by fome of the chemical writers to the flowers of zink.

This fubftance, diflblved in vinegar, affords what they have in their unintelligible language called, oil of Talc, and extolled as a thing of vaft power in the fixing of Mercury, and many other imaginary operations ; and befiderhis, they call it a fo- vereign remedy for all dtfeafes.

The chemifts of after ages, feeing fuch prodigious effects afcribed to oil of Talc, and not conceiving that Talc was a

mere