TALC. 



"f ale i» divided by fome mineralogifts into three fub- 

 fpecics, -uiz. common talc, indurated talc, and columnar 

 talc. 



Common laic; laic lamlnaire, Hauy. Its colours arc thole 

 before enumerated, but tiie green fometimes pafTes into 

 dark blue. The laminx are very tender and flexible, hut 

 not elaftic : by this they may be diftinguifhed from the 

 laminx of mica, which ponifs a confiderable degree of elaf- 

 licity. In France tliis talc is called craie de Briangon ; it is 

 found in confiderable mafles in rocks of ferpentine, accom- 

 panied with aftinolite, granular lime-ftone, and dolomite, 

 along with indurated talc. The conftiluent parts are as 

 follow : 



Vsuquelin- Klaprotb. 



Silcx .... 62 61.75 



Magnefia - - - 27 30.J0 



Alumine ... i.jo 



Potafh .... 2.75 



^ Oxyd of iron - - - 3.50 2.50 



* Water .... d 2.25 



It is found in Aberdeenfliire and BamfTlhiie, in Scotland, 

 and in various parts of the continent of Europe, where rocks 

 of ferpentine and porphyry occur. The talc which is 

 brought from the mountains of the Tyrol is called in com- 

 merce Venetian laic. 



Talc enters largely into the corapofition of the cofmetic 

 named rouge. This fubftance is prepared by rubbing to. 

 gethcr in a wai-m mortar, generally of ierpentine, certain 

 proportions of carmine and finely powdered talc, with a 

 fmall portion of oil of benzoin. The Romans prepared a 

 beautiful blue or purple colour, by combining this fubftance 

 with the colouring fluid of the buccinum reticulatum and 

 buccinum lapillus, teftaceous animals abounding on the 

 coafts of the Mediterranean. The flefli-coloured polifh on 

 figures made of gypfum is given by rubbing them with talc. 

 The Perfians, according to Tavernier, whiten the walls of 

 their houfes by means of lime-water, and then powder them 

 with filver.coloured talc. Talc has fometimes been ufed 

 medicinally by the Chinefe and Europeans. 



The chief ufe of the Ruffian is as a fcreen or cover for 

 paintings in miniature and crayons ; to- which purpofe thin 

 dices of it are ufed. The Venetian is fometimes alfo ufed 

 for a fucus ; in order to which, by reafon of the difficulty 

 of pulverizing it, &c. they content themfelves to rafp it 

 with the flcin of a fea-dog, and to pafs the rafpings through 

 a fieve. 



Phny, in his Natural Hiftory, lib. xxxvi. c. 22. obferves, 

 that the Romans not only ufed the Ruffian fort for window- 

 lights, but they alfo paved the circus with a kind of it. 

 See Glass, 



Indurated talc is lefs flexible and lefs tranflucent than the 

 preceding : it occurs in nialTes, and has fometimes a radiated 

 ftruclure ; its colours are various fliades of green and 

 greenirti-grey. It forms beds of confiderable fize in moun- 

 tains of gneifs, mica-flate, and ferpentine ; it approaches 

 nearly to pot-ftone, and even to fteatite, in many of its cha- 

 rafters. It occurs in Perthfliire and Bamff'ftiire, in Scotland, 

 and in France, Sweden, Saxony, Siberia, the Tyrol, and 

 Switzerland. It is employed for drawing lines by car- 

 penters, taylors, hat-makers, and glaziers. It is fometimes 

 made into culinary vefTels, like pot-fl:one, and is employed 

 in powder for removing ftains of greafe from filk. 



Columnar talc occurs in thin columnar prifmatic concre- 

 tions, and it is opaque, The connedlion between talc, 

 iifteftus, pot-ftone, ferpentine, chlorite, and even mica, may 



be traced by their apptfent graduation into each other, par- 

 ticularly in fome of the rock formations. See Asbestus, 

 Pot-stone, &c. 



The mixture of talc with different kinds and quantities of 

 "■lafs may be fuccefsfuUy 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 be- 

 come a firm and fohd mafs of a brOwn colour. Minium, or 

 glafs of lead, mixed in equal quantities with talc, and fet in 

 a violent fire, runs into a yellowifti glafs, refembling the 

 opaque 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 fcarcely vitrifiable 

 by any fire : hence appears the reafon why copels made of 

 lime and talc are fo very hard to vitrify. Minium, added 

 to thefe mixtures, make them combine into a firm mafs, but 

 without perfeft fufion ; but borax added to them, melts 

 them readily into a truo glafs. The gypfeous 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 gypfeous matter 

 called glacies Mariie, or the common plated fpar, with one 

 part of borax, run into a yellow mafs refembling a topaz. 



The argillaceous earths do not vitrify with talc ; but th^y 

 run into a mafs of great hardnefs, which will give fire witis 

 fteel, and is very ferviceable to make crucibles of, thefs 

 veflfels not fuffering the glafs of lead to run through them.. 

 Talc, joined with the vitrifiable ftones, fonns no remarkable 

 body, but the mafs remains friable ; but from thefe maffes, 

 by the addition of proper matter to render them fluid, great 

 variety of elegant compounds may be made. Thus if talc be 

 mixed in equal quantities with powder of flints, on adding 

 to the whole a fourth part of cryftal-glafs, the whole unites 

 into an opaque but fohd wliite mafs. Alkali-falt, 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 quantities, the refemblances ef many 

 beautiful ftones are produced ; and what is very remarkable, 

 fome grains of metalline mattej' are often found on the fur» 

 face of the mafles. 



Caefalpinus, Aldrovand, and fome others affirm, that talc 

 melted with copper, or added to copper, while in fufion, 

 gave it a white colour : tliis being taken for granted, authors' 

 have hence agreed that talc contains an arfenical earth. But 

 experiment (hews this to have been a fajfe afTertion, in regard 

 to talc ; and probably it only owes its origin to the cant lan- 

 guage of fome of the alchemifts, who have called the flowers 

 of zinc talc, though thefe alone muft 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 ; and with bifmuth it calcines into 

 a grey powder. So little is there in the propofals of the 

 cnemifts for the metaUization of talc by antimony and bifi 

 muth. Mem. de I'Acad. de Berlin, Ann. 1746. 



In what part of Mr. Boyle's works the learned author, 

 from whom the foregoing extraft 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. Boyle fays, that 

 the calcination of talc is fo very difficult, that eminent che^ 

 mifts have looked upon calxes of talc as counterfeits. 

 Works abr. vol. i. p. 160. 



Mr. Boyle mentions the extraAing of gold from talc, as 



^ hiring 



