TELLURIUM. 



where it has hitherto only been found. It is fo called, frupi 

 the particular appearance formed by the aggregation of the 

 cs^llals ; it occurs in veins in porphyry. 1 he colour of gra- 

 phic tellurium is fteel-grey, which is foitiotimcs varioufly 

 taniifhed by expofure to the air : it is alfo found wiiite, 

 yellow, or lead-grey. It has a fhining metaUic luftre. It 

 occurs maffive, diOminated in leaves, and cryftalhzcd in 

 fmall comprcflcd hcxalicdral prifms, eitlier witli or without 

 tetrahedral fummits, and generally arranged in rows on the 

 furface of quartz. There are frequently other prifms at- 

 tached to the extremities of tlie former, at right angles with 

 them, giving the whole row an appearance of Pcrfepolitan 

 charaaers. The planes of the cryllals arc fmooth. " The 

 maffive variety, which is very rare, occurs in granulai- diftinft 

 concretions." (Jamefon's Min.) It is foft, brittle, and 

 frangible, and yields a lead-grey itrcak. The fpecific gra- 

 vity is 5.723. Before the blow-pipe it burns with a green 

 flame, and is volatilized. The conilituent parts, accerding 

 to Klaproth, are 



Tellurium - . ... 60 



Gold ------ JO 



Silver ------ 10 



Tclloiv Tfl/iirium Ore. — The colour of this ore is filver- 

 white, paffing into yellow ifli or brafs-white and grey. It oc- 

 aurs in grains, and in minute comprefled four-fided prifms, 

 with a lamellar ftruclure and bright metallic luftre : it alfo oc- 

 curs maffive and reticulated : it is foft and fomewhat fedlile : 

 the fpecific gravity is 10.878. The conftituent parts, ac- 

 cording to Klaproth, are 



Tellurium - - - - 44- 7 J 



Gold 26.75 



Lead . - . . . iq.j 



Silver - . . . . 8.5 



Sulphur . - . - . ^ 



This ore, which is worked for the gold and filver it con- 

 tains, has liitherto been fouud only at Nagyag, in Tranfyl- 

 vania. It occurs in fmall irregular veins in porphyry. The 

 moft frequent vein-ftones are brown fpar and quartz : it is 

 fometimes afTociated with red manganefe ore, fulphuret of 

 manganefe, native arfenic, plumofe antimony, and native gold. 

 Bloii Tellurium Ore; NagyagerK, Werner. — The colour 

 ef this ore is between iron-black and dark lc?.d-grey. It 

 occurs maffive and in leaves, and alfo crytlallizcd, in the fol- 

 lowing forms ; oblique four-fided tables, redlangular four- 

 lided tables, fix and eight-fided tables, and in acute oftohe- 

 drpns acuminated at the Tummit. It has a fplendent me- 

 talhc luftre, a more or lefs curved lamellar ftrufture, with 

 joints on cleavage in one direflion. It yields eafily to the 

 knife, and is feftile : the thin laminas are flexible ; it ftains 

 flightiy when rubbed in the fingers. The fpecific gravity 

 is 8.919. This ore melts very eafily before tbe blow-pipe ; 

 the fulphur and tellurium are volatilized ; a blackifh round- 

 coloured globule remains, which, on being molted with 

 borax, yields a globule which confifts of gold alloyed with 

 filver ; the flag which remains tinges borax violet-blue. It* 

 conftituent parts, according to Klaproth, aie 

 Tellurium - - - - 

 Lead .... 



Gold 

 Silver 

 Copper 

 Sulphur 



32.2 

 54.0 

 9.0 

 0.5 



1-3 



3-0 



This ore is found affociated with the preceding ore of 

 tellurium. An ore of tellurium has lately been difcovercd 

 in Norway by Efmark. An account of the mines where 

 tellurium is obtjuncd, was publifhcd by M. Stutr in the new 

 Memoirs of the Society of Naluralifts at Berlin, vol. ii. 



1799, and by Efmark, entitled " An Account of a Mine- 

 ralogical Journey through Hung-iry, Traafylvania, and the 

 Bannat," in tha Neuen Bergmannillchcn Journal, vuk. i. 

 and ii. Dr. Clarke, in the 4tli vol. of lii« Travels, has alfo 

 recently given a dcfcription of the tellurium mines, from 

 which we Iliall briefly cxtraft the moft intcrcfting partkubiri 

 at the clofc of the prcfent article. 



Analyju of the Ores of Tellurium. — Thcfe orc8 are worked 

 for ulie gold and filver tlicy contain ; and tlie tellurium with 

 wliich they are combined being extremely volatile at a low 

 degree of heat, tliis metal was loft in the proccfs of cxiraftion, 

 and was for a long time fuppufcd to be antimony. Muller iirfl 

 fufpcfted that it was a new metal. Bcrgmann made fovcral 

 experiments upon it, but left thequcftion undecided. 



Klaproth, in 1798, read an account of the difcovrry of 

 this new metal in the public fitting of the Royal Acadany 

 of Sciences at Berlin. 



The proccfs of extraSing the metal from native telluriuni 

 is as follows. Six parts of muriatic acid are poured on the 

 crude ore, which has been previoufly fcparated as mucli as 

 poflible from its matrix, and mechanically divided. Heat is 

 applied, and three parts of nitric acid arc added by degrees. 

 A violent effervefcence takes place. By this proceis the 

 metallic portion of the o're is djlTolvcd, leaving the m.itrix, 

 which is principally quartz, behind. In the next place, tlw 

 filtered folution is carefully diluted with as much water as 

 it will bear without being rendered turbid. Cauflic potafh 

 or foda is added, until the precipitate which is firft produced 

 difappears, and only a dark-brown flimy rcfiduc rcmsuns. 



Decant the folution, fetting the refiduum apart for fub- 

 fequent examination : it confifts of iron and gold. To the 

 alkaline folution add muriatic acid, until it be faturated, 

 moft accurately obfcrving the point of faturation. A copi- 

 ous white precipitate eniues, which in a raifcd temperature 

 falls to the bottom of the vcftel in the form of a heavy 

 powder. It is then coUefted, and wafhcd with equal parts 

 of water and fpirits of wine, and dried in a gentle warmth. 

 This is the oxyd of tellurium. To reduce it to a metallic 

 form, it (liould be heated in a fmall glafs retort along witK 

 one-twelfth of its weight of charcoal, or it may be previ- 

 oufly moiftened with oil. Adapt a receiver to the retort, 

 and let heat be applied till the powder be brought to a ftate 

 of ignition. Small metalhc drops will be feen hning the 

 upper part of the retort, which fall down feparalely, and 

 arc fucceeded by others. On refrigeration, the reduced 

 metal (excepting fome few metallic drops on the flioiildcr 

 of the retort) is found fufed, with a clean fplendent furface, 

 which is moft frequently cry ftalllne. At the moment the reduc- 

 tion takes place, a quantity of carbonic acid gas is fuddenly 

 generated, carr)'ing along with it fome particles of the mixture, 

 which it depofits in the receiver. The other ores of tellurium 

 being worked as gold ore ; for their analyfis, fee Gold. 



Tellurium in the pure reguline ftate was firft obtained by 

 Klaproth, who has given the following dcfcription of it : 

 il is of a tin-white colour, verging to lead-grey ; it has a very 

 high metallic fplcndour, and a foliated ftrudurc ; the furfaccs 

 of tlie fragments are very brilliant. When cooling flowly 

 after fuflon, it an"umes a cryftalline furface. It is very 

 brittle, and eafily reduced to powder. Among all the known 

 fufible metals, except the metalline alkalies or earths, tellu- 

 rium poflefles the leart fpecific gravity, being only 6.185. 



Tellurium melts fooner thau antimony, when expofed to 

 the fame degree of heat, but later than lead. It inflames 

 upon charcoal before the blowpipe with a violence rcfem- 

 bling detonation, and with a vivid light-blue flame, which on 

 the edges has a grecnifli tinge. By the continued aftion of 

 the blowpipe, it is entirely diffipated in a greyiftl-whitc 

 vapour, and emJU a fraell hke that of fcraped radifli. 



Q q t Tellurium 



