CHEMICAL PRINCIPLES 
353 
entirely eftected, forming small crystals of the most beautiful Oxides ofirt Id. 
metallic brilliancy, and extremely light. The liquor in which 
this metallic powder was suspended had much resemblance to 
the avanturine. Its tetherous smell proved that the reduction of 
the gold was owing to the presence of a small quantity of al- 
cohol. I have related this experiment, because it furnishes us 
with the means of reducing gold, with its true colour and 
metallic brightness, to a state of the greatest possible mecha- N- B- 
nical division. If mixed in this state with a little of the solu- 
tion of gum arabic, it may be employed in miniature painting 
and may be burnished. In the preparations of gold of M. Chris- 
tien, I employed it instead of the metallic gold reduced accord- 
ing to the prescription from an amalgam of gold by the means of 
a concave mirror. 
3. Gold combined with tin. Purple of Cassius. 
(a) A solution of neutral muriat of gold, mixed with a 
solution of murias stannosus, diluted with a small portion of 
water, produced a precipitate of a deep brown, almost a black, 
which had no trace of metallic brightness. After it bad been 
placed on a filtre and well washed, 1 caused it to be dried. When 
examined by crushing it on a polished steel plate, it appeared of 
a metallic brightness, .and of a pale yellow colour. On being 
melted with borax, it produced a metallic button, almost white, 
or approaching to a yellow. This metallic button, when dis- 
solved in the nitro-muriatic acid, gave a solution of a yellow 
colour, and containing tin. It also afforded a great quantity of 
the oxide of tin, not dissolved. The precipitate was therefore 
a metallic alloy of gold and tin; and in ihe expeiiment 
by which they were produced, the mutual affinity of the gold 
and the tin had caused a reduction of a portion of the tin, of 
the murias stannosus, by means of another portion of the 
same. (b) A solution of muri.ite of gold, mixed with 
an extremely dilute solution of the muria.s stannosus, produced, 
first of all, a red liquid, from which a purple precipitate was 
slowly deposited. Ihis precipitate, on being washed and 
diied, was entirely soluble in caustic ammonia, and conse- 
D d 2 quently 
