138 Chemistry and Chemical Arts. 
heat in a porcelain tube, traversed by a current of hydrogen gas. 
Tellurium, although so difficult to sublime when heated alone in a 
porcelain retort, is volatilized very readily in a current of this gas. 
There remains in the capsule a small quantity of telluret of gold, of 
copper, of iron and of manganese. ‘There is volatilized along with 
the tellurium, a small quantity of selenium, which is wholly deposit- 
ed at the extremity of the tube, under the form of a red powder. 
In order to separate all traces of this body, it is necessary to oxidate 
and calcine the substance ; by which means all the selenium is vola- 
tilized in the state of selenious acid. 
The telluret of silver cannot be treated in the same way. In or- 
der to extract the tellurium or to analyze it, it is necessary to heat it 
moderately in a current of chlorine, to receive the chloride of tellu- 
rium in water, acidulated by muriatic acid, to precipitate the tellu- 
rium by sulphite of soda, and afterwards to sublime it in hydro- 
as. ; 
Tellurium contracts much in passing from the liquid to the solid 
state, on which account, it often contains cavities. When free from 
these its Sp. gr. =6.2445. 
It hastwo degrees of oxidation, Ist. the oxide, or tellurious acid ; 
Qndly. telluric acid. 
- The tellurious acid presents itself under two modifications A and 
B. Variety A is produced when the tellurium is dissolved in nitric 
acid ; it exists in the solution so long as it is rendered turbid by wa- 
ter, after which the liquid contains only variety B. The precipitate 
Avis pure anhydrous tellurious acid: it melts into a transparent yel- 
low fluid, which on cooling becomes a white, crystalline mass. It 
has a feebly metallic taste. It slightly reddens turnsole ; it is near- 
ly insoluble in the acids and in ammonia; nor does it dissolve in the 
alkaline carbonates, except by the aid of heat. 
Variety B is obtained by melting tellurious acid with an alkaline 
carbonate, dissolving the fused mass in water and adding nitric acid 
until the liquid becomes slightly acid. The precipitate is an hy- 
drate. It is in flocculi, white, and possessed of a metallic taste; it 
reddens turnsole, and is slightly soluble in water. It dissolves read- 
ily in the acids, in ammonia, and in the alkaline carbonates, from 
which it expels the carbonic acid. When heated to a temperature 
above twenty C. it changes to variety A. We are acquainted at 
present with no salts except such as are formed by variety B, of 
which there are those containing one, two and four atoms of acid 
for one of base. 
