46 
SELECTED ARTICLES. 
of copaiba, we may consider the crystallised resin of copaiba 
likewise to be an oxide. We therefore see that isomeric bo- 
dies, when oxidized may afford isomeric oxides. 
The composition of the resin of copaiba, like that of colo- 
phane may be expressed by the formula, 10 C-f-16 H + 0. Its 
composition, calculated from this formula, would be, carbon 
79.275, hydrogen 10.355, oxygen 10.37. 
If ammonia be added to a solution of resin of copaiba in al- 
cohol, no precipitate is formed, as takes place with the gene- 
rality of the solutions of the acid resins; if the resin be pre- 
cipitated by water, the ammonia readily dissolves the pre- 
cipitate. A solution of potash in alcohol has no effect on the 
alcoholic solution of the resin. A mixture of a spirituous so- 
lution of the resin and of a concentrated aqueous solution of 
potash may be made in all proportions, without any action 
taking place; but if more water be added, the combination of 
resin and potash is precipitated with an excess of the base. 
An alcoholic solution of the resin is not disturbed on the 
addition of an alcoholic solution of nitrate of silver; but if a 
little ammonia be added a precipitate takes place, formed of a 
combination of resin and oxide of silver, which is redissolved 
by an excess of ammonia. The precipitate is crystalline, and 
preserves this structure even after being dried; it dissolves in 
alcohol though with difficulty; exposure to light alters its co- 
lour, as it does the other salts of silver; it melts at a low heat 
like a resin; if the temperature be increased, it is decom- 
posed, leaving a residue of metallic silver after the combustion 
of the charcoal. 
M. Rose obtained the following proportions of silver in 
three different experiments: 
1. 0.308 grammes gave 0.081 silver 
2. 0.321 0.082 
3. 0.376 0.096 or 
1st 
Oxide of silver, 28.25 
Resin, 71:75 
2d. 3d. 
27.41 27.40 
72.59 72.60 
