TELLUROUS ACID. 623 



vania ; but it has been found lately, in considerable abundance, 

 at Schemnitz, in Hungary, combined with bismuth ; and in the 

 silver mine of Sadovinski in the Altai, united with silver and 

 with lead. It was first described as a new metal by Klaproth, 

 who gave it the name tellurium, from tellus, the earth. Tellu- 

 rium is separated from the foreign bodies with which it is mixed 

 and combined in its ores, by processes of a very complicated 

 nature. (Berzelius, Traite, I. 344.) 



In a state of purity, tellurium is silver-white and very bril- 

 liant. It is very crystallizable, assuming a rhombohedral form, 

 in which it is isomorphous with arsenic and antimony. It is 

 brittle, and an indifferent conductor of heat and electricity for a 

 metal. Its density is from 6.2324 to 6.2578, according to 

 Berzelius. Tellurium is about as fusible as antimony; at a 

 higher temperature it may be distilled. It burns in air, at a 

 high temperature, with a lively blue flame, green at the borders, 

 and diffuses a dense white smoke, which generally has the odour 

 of decaying horse-radish, from the presence of a little selenium. 

 Tellurium belongs to the sulphur class of elements. Like sele- 

 nium and sulphur, it dissolves to a small extent in concentrated 

 sulphuric acid, and communicates to it a fine purple red colour. 

 In this solution, the metal is not oxidated, for it is precipitated 

 again, in the metallic state, by water. This metal has also 

 considerable analogy with antimony, and may probably connect 

 together the sulphur and phosphorus families. Tellurium com- 

 bines in two proportions with oxygen, forming tellurous acid, 

 TeO 2 , and telluric acid, TeO 3 . 



Tellurous acid, TeO 2 ; 1001.8 or 80.?5. This acid differs 

 remarkably in properties according as it is anhydrous or hydrated, 

 forming two isomeric modifications of the same acid, of which 

 the anhydrous acid has been named alphatellurous acid, and the 

 hydrated betatellurous, by Berzelius, to whom we are indebted 

 for nearly all our accurate knowledge of the acids of tellurium. 

 But a sufficient distinction will be made between these bodies 

 by retaining one of these terms, alphatellurous, as applied 

 to the anhydrous acid, and confining the term tellurous acid to 

 the hydrated acid. The proper tellurous acid then is obtained 

 by precipitating the bichloride of tellurium by cold water ; or 

 by fusing anhydrous tellurous acid with an equal weight of car- 

 bonate of potash, so long as carbonic acid is disengaged, dis- 

 solving the tellurite of potash in water, and adding nitric acid 



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