REPORT ON CHEMISTRY. 473 
nated alkalies. It contains 12*47 per cent, of water, and the 
dry acid is composed of, 
Tellurium 80*06 = 1 atom. 
Oxygen . 19*94 = 2 atoms. 
It forms bi- and quadri- tellurets, the latter most easily. 
Telluric acid. —The tellurous acid in solution with excess of 
caustic alkali is submitted to a current of chlorine, till the pre¬ 
cipitate, which at first falls, is entirely redissolved. Chloride of 
barium is added to precipitate any sulphuric or selenic acid 
which may be present, after which the solution is saturated with 
ammonia, and the tellurate of barytes precipitated by chloride 
of barium, collected and washed with cold water. This salt is 
decomposed by sulphuric acid, and the concentrated solution 
deposits the telluric acid in beautiful prismatic crystals. 
Tellurous acid may also be oxidized by fusion with nitrate of 
potash, when on treating with water paratellurate of potash 
remains undissolved. This may be dissolved in nitric acid sa¬ 
turated with ammonia and precipitated by a barytes or lead 
salt as before. » 
The acid crystallizes in six-sided prisms terminated by four 
planes, has a metallic taste resembling that of nitrate of silver, 
dissolves slowly in cold but rapidly and in large quantity in 
boiling water. It is very sparingly soluble in alcohol. The 
• 
crystals contain three atoms of water, being (T + 3 0) + 3H. 
At 212° it loses no water ; on a hot sand-bath it loses two atoms, 
retaining its crystalline form ; and is insoluble in cold water. At 
a temperature below redness it loses the third atom of water 
and gives a beautiful yellow acid which still retains the crystal¬ 
line form. At a higher temperature it loses an atom of oxygen, 
becoming paratellurous acid. 
The yellow acid obtained by heating below redness is the 
paratelluric acid. It is insoluble in boiling water and boiling 
caustic ley if not very concentrated, in cold concentrated muri¬ 
atic and in boiling nitric acid. From the concentrated caustic 
potash solution it is obtained in the usual state. It gives bi- 
and quadri- salts, those of the common and metameric acid 
differing in properties. 
The hydrated crystals, as they are at first formed, contain 
23*428 per cent. = 3 atoms of water; after drying on a hot 
sand-bath 9*255 per cent. = 1 atom of water; and the anhydrous 
acid consists of 
Tellurium 72*799 = 1 atom, 
Oxygen . 27*201 = 3 atoms. 
