104 
PREPARATION OF THE OXIDE OF GOLD. 
obtained is very heavy, and easily washed by decantation. 
Jt is washed until the waters cease to be precipitated by 
sulphuric acid ; the aurate of baryta is then treated with 
nitric acid diluted with water, which sets the oxide of gold 
free. It is requisite to heat the liquid to boiling, and to 
keep it at this temperature for some minutes, in order to 
decompose the last traces of the baryta salt. On washing 
by decantation until the water no longer reddens litmus- 
paper, the oxide is obtained pure. 
By whichever process tlie oxide of gold is obtained, par- 
ticular attention must be paid to the mode of drying it. 
The temperature of boiling water, which is sometimes used, 
frequently reduces a part of it. It may be dried in vacuo 
or under a bell-glass over sulphuric acid ; but the most 
simple plan is to press it between folds of blotting-paper, 
and to expose it to the air protected from the light. 
I may briefly notice, before concluding, the best method 
of obtaining the gold from the liquids resulting from these 
operations. The liquids resulting from washing the aurate 
of baryta must not be mixed with those obtained in wash^ 
ing the oxide. The first contain far more gold. They are 
concentrated by evaporation, and the baryta precipitated 
by sulphuric acid ; the liquid, after standing, is decanted, 
and a solution of protosulphate of iron added to it, which 
precipitates the Avhole of the gold. The waters derived 
from washing the oxide are also evaporated and precipi- 
tated by sulphuric acid ; but they must not be treated 
immediately with protosulphate of iron, on account of the 
action which the free nitric acid they contain, exerts upon 
this salt. After precipitation with sulphuric acid, the liquid 
is decanted and evaporated to dryness, and the small 
residue obtained treated with nitromuriatic acid. This 
solution is evaporated nearly to dryness to expel the nitric 
acid, then diluted with water, and treated with sulphate of 
iron. — Chem. Gaz. from Journ, de Pharm. 
