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PREPARATION OP THE OXIDE OP GOLD. 
103 
likewise that which yields the purest oxide. The oxide of 
gold obtained by carbonate of soda retains a certain 
quantity of alkaline carbonate, which cannot be removed 
by washing. On decomposing a little of the oxide by heat, 
and exhausting the gold with hydrochloric acid, the liquid 
leaves on evaporation a residue of chloride of sodium, 
while the oxide prepared with chloride of barium affords 
no appreciable residue when treated in the same manner, 
and the solution is scarcely rendered turbid by sulphuric 
acid. The process is moreover so rapid and simple of ex- 
ecution, that on this account alone it appears to me prefer- 
able to the two others, especially to Pelletier's, which, as 
is well known, is long and tedious on account of the large 
bulk of the raagnesian precipitate and of tlie time required 
for washing. I think it may be useful therefore to describe 
this new process at some length, especially as the only 
account of it hitherto published is a brief notice in the new 
edition of Soubeiran's *' Traite de Pharmacie": — 1 part of 
gold is dissolved in 4 parts of nitromuriatic acid, the solu- 
tion evaporated to dryness, redissolved in water, which 
leaves a slight residue of metallic gold and of protochloride, 
which is redissolved with a little nitromuriatic acid. This 
solution is again evaporated to dryness, and redissolved in 
water. The solution of the chloride of gold, which is thus 
obtained quite free from acid, is mixed with pure potash 
(perfectly free from chloride) until it has a strong alkaline 
reaction upon curcuma-paper. It immediately becomes 
turbid; the solution is then mixed with chloride of barium, 
which instantly yields a canary-yellow precipitate of aurate 
of baryta. The addition of chloride of barium is dis- 
continued when the precipitate begins to appear slightly- 
white, which shows that the whole of the oxide of gold 
being precipitated, the alkali has begun to act upon the 
baryta of the chloride of barium. The supernatant liquid 
is colourless; consequently the metal is almost entirely- 
precipitated from its solution. The aurate of baryta thus 
