472 
SECOND REPORT -1832. 
silver. The solution of the chloride in muriatic acid is precipi¬ 
tated by hyposulphite of soda, and the precipitate, as before, 
distilled in hydrogen gas. In this way it may contain selenium, 
the most of which is carried over by the hydrogen gas in the 
form of a red vapour ; hut it cannot be obtained by this process 
entirely free from selenium, unless it have been previously 
heated to fusion in the state of oxide, by which the selenious 
acid is driven off. 
Metallic tellurium. —Pure tellurium heated to full redness in 
a close vessel volatilizes in the form of a yellow gas, which con¬ 
denses again in drops, and on cooling crystallizes in forms which 
appear to belong to the regular system. The smell of the va¬ 
pour is peculiar, slightly resembling that of selenium. Its spe¬ 
cific gravity, taking the mean of several trials, is 6*2455 ; the 
highest was 6*2578, and is probably nearest the truth. 
Its atomic weight, taking the mean of four results, is 802*902. 
The mean of two nearly coinciding results gives 801*7675. 
Berzelius did not succeed in forming; an oxide containing' one 
atom of oxygen T, but he obtained two degrees of oxidation, 
»• ••• 
the one formerly known T, and a higher one T, which is the 
telluric acid. 
Tellurous acid. —T can scarcely ever be made to act the 
part of a base, and therefore it must be considered as an acid, 
—the tellurous acid. Like oxide of tin, it takes two isomeric 
forms, which possess unlike properties. Prepared by digesting 
tellurium with nitric acid, and precipitating the solution by 
water or allowing it to crystallize, it is paratellurous acid ( acidum 
paratellurosum). In this state it crystallizes apparently in octo- 
hasdrons, contains no water, is almost insoluble in nitric acid, and 
when precipitated by water, and dried on the water-bath, is 
milk white and crystalline. It reddens litmus slowly, and is 
very sparingly soluble in water. On heating it becomes yellow, 
and an incipient redness melts into a clear liquid, is volatilized 
in small quantity, and cools into a milk-white crystalline mass 
of acid in the same metameric state. By slow cooling it may 
be obtained in a transparent mass. 
By dissolving this mass in muriatic acid, or more easily by 
fusing it with the proper quantity of carbonate of soda to form 
a neutral salt, and precipitating its solution with nitric acid, the 
tellurous acid ( acidum tellurosum ) is obtained in the state of a 
voluminous flocky precipitate. This must be dried in the air, 
for if it be even slightly heated it loses its water and becomes 
metameric . 
In this state it is soluble in acids, in ammonia and in carbo- 
