Chemistry and Chemical Arts. 139 
In order to obtain telluric acid, a mixture of equal parts of tellu- 
rious acid and of carbonate of potash is melted together; the mass 
is dissolved in water and to it is added a quantity of hydrate of pot- 
ash containing at least as much alkali as the fused mass, when a cur- 
rent of chlorine is passed through it until the chlorine is in excess, 
and until the precipitate which is at first formed, is completely re- 
dissolved ; to the liquid is then added a small quantity of chloride of 
barium, which removes from it the sulphuric and the selenic acid it 
may contain: it is-filtered and ammonia being added in slight excess, 
and afterwards chloride of barium, all the telluric acid is precipita- 
ted. The precipitate, at first bulky, shortly becomes granular and 
dense. It is washed, and dried by a gentle heat, and digested with 
one quarter of its weight of concentrated sulphuric acid, previously 
diluted with water, the liquid is concentrated, and finally left to 
spontaneous evaporation, when the acid is deposited in crystals hav- 
ing the form of flattened, four sided prisms, terminated by very low 
quadrilateral pyramids. 
In this state, the telluric acid contains 0.225 of water, which it 
does not give up at 100° C. Ata more elevated heat, but much 
below that of redness, it loses two thirds, or 0.155 without losing its 
form. Heated still more intensely, it becomes anhydrous and is 
converted into a citron yellow powder, which is a variety of the acid 
resembling variety A of the tellurious acid. Finally, when heated 
sufficiently, it gives up its oxygen and leaves behind a pulverulent, 
snow-white tellurious acid. 7 
The telluric acid B is always soluble in water ; when two thirds 
of its water is expelled, it is still soluble, but slowly. The anhy- 
‘drous acid A is insoluble in all the acids. It dissolves in muriatic 
acid with the disengagement of chlorine, but with difficulty, and re- 
quiring the aid of heat. Telluric acid in solution is decomposed by 
sulphuretted hydrogen, not instantly, but slowly, and only with the 
aid of heat. 
This acid possesses like the tellurious, a tendency to form salts 
which contain one, two and four atoms of acid, to one of base. By 
the action of heat, salts of the modification B are changed into salts 
of the variety A, afterwards they change inio tellurites with the dis- 
engagement of oxygen, a red heat, however, is necessary to effect 
this transformation. When tellurious acid is heated with nitre at 
a temperature below redness, and so long as it disengages nitrous gas, 
and afterwards washed with water, there remains a citron yellow 
