624 TELLUROUS ACID. 



to it, till the liquor distinctly reddens litmus paper. A white 

 and bulky precipitate is produced, which is washed with ice-cold 

 water, and afterwards dried without artificial heat. Tellurium 

 likewise dissolves with violence in pure nitric acid of density 

 1.25, and if after the first five minutes, the clear liquid be poured 

 into water, tellurous acid is precipitated in white flocks. But if 

 not immediately precipitated, the nitric acid solution undergoes 

 a change. 



The hydrated acid obtained by these processes forms a light, 

 white, earthy mass, of a bitter and metallic taste. It instantly 

 reddens litmus paper, and while still humid, dissolves to a sen- 

 sible extent in water. It is very soluble in acids, and these 

 solutions are not subject to change, except that in nitric acid. 

 Ammonia and the alkaline carbonates also dissolve it easily, the 

 latter becoming bicarbonates. It is this tellurous acid which 

 plays the part of acid in the tellurites, and also that of base in 

 some compounds which the tellurous, like vanadic, tungstic, 

 and molybdic acids, forms with the stronger acids. The tellu- 

 rites of potash and soda, which are neutral in composition, are 

 very soluble, and have a strong alkaline reaction ; their solu- 

 tions are decomposed by the carbonic acid of the air. 



Alphatellurous acid. When the solution of tellurous acid in 

 water is heated to 104, it deposits alphatellurous acid in grains, 

 and loses its acid reaction. The same change occurs when it is 

 attempted to dry the hydrated tellurous acid by heat. It parts 

 with combined water, and becomes granular. The solution of 

 tellurous acid in nitric acid changes spontaneously -in a few 

 hours, and in a quarter of an hour when heat is applied to it, 

 and allows the alphatellurous acid to precipitate* When the 

 deposition of the acid is slow, it forms a crystalline mass of fine 

 grains, among which octohedral crystals may be perceived by 

 the microscope. The acid is then anhydrous. Alphatellurous 

 acid does not redden litmus, or not till after a time. It is but 

 very slightly soluble in water; the solution has no acid reaction. 

 No salts of alphatellurous have been formed in the humid 

 way, although from its analogy to a corresponding telluric acid, 

 it is probable that such salts may exist. At a low red heat, it 

 fuses into a clear transparent liquid of a deep yellow colour, 

 which on cooling becomes a white and highly crystalline mass, 

 easily detached from a crucible. Tellurous acid is volatile, 

 although less so than the metal itself. 



