1817.) during the Year 1816. 29 
X. METALS. 
1. Gold.—The solution of gold in aqua regia has long been 
familiarly known to chemists, though the examination of it has 
been hitherto so difficult that chemists contradict one another re- 
specting the effect produced by the addition of alkalies. According 
to Vauquelin, Duportal, and Pelletier, the alkalies do not occasion 
a precipitation when poured into this liquid cold. Oberkampf ob- 
tained a contrary result. According to M. Figuier, a precipitation 
always takes place, and it makes no difference whether the liquid 
contains an excess of acid or not; except that in the former case a 
greater proportion of alkali is requisite; for the precipitate never 
appears unless there be an excess of alkali. Six grammes of dry 
muriate of gold were dissolved in 150 grammes of distilled water. 
The solution was divided into two equal parts, and put into two 
conical glasses. Into the one were put four grammes of muriatic 
acid. Both were saturated with a solution of caustic potash. The 
colour became red, and a grey-coloured flocky precipitate gradually 
fell. This precipitate was at its maximum in 48 hours. ‘It was the 
same in each glass. Being separated by the filter, the liquids were 
heated. New precipitates fell, much darker in their colour. The 
whole being united and dried, were found to represent in each two 
thirds of the gold held in solution. On adding muriatic acid to 
each solution, the yellow colour was restored. Potash occasioned a 
new precipitate in each; and by adding muriatic acid and potash 
alternately, the whole gold was precipitated. (Ann. de Chim. et 
Phys. ii. 102.) How is this precipitation to be explained ? 
2. Purification of crude Platinum.—The Marquis of Ridolfi has 
tried the following method of separating the foreign metals with 
which crude platinum is alloyed. He fuses it with half its weight 
of lead, reduces the alloy to powder, mixes it with sulphur, and 
exposes it to a strong heat in a covered crucible. A brittle button 
was obtained, consisting of platinum, lead, and sulphur. It was 
fused with a small addition of lead, heated to whiteness, and ham- 
mered in that state with a hot hammer upon a hot anvil. By this 
means the lead was forced out in a state of fusion, The platinum 
thus obtained was ductile and malleable, and of the specific gravity 
22630. (Journal of the Royal Institution, i.259.) From various 
trials which I have made, I have reason to believe that the specific 
gravity of pure platinum well hammered is 21°65. It is just pos- 
sible, though not probable, that the specific gravity of the specimen 
examined by Ridolfi was increased by its being alloyed with a little 
lead. 
3. Cupellation of Silver.—M. d’Arcet has published the follow- 
ing table, indicating from his own experiments the proportion of 
lead necessary for the cupellation of silver of different degrees of 
fineness. (Ann, de Chim. et Phys. i. 75.) 
