50 
SELECTED ARTICLES. 
way as that with the crystalline resin. 0.6255 grammes of 
this combination gave on analysis, 0.0275 grammes of oxide 
of lead, and 0.133 grammes of lead, it is therefore composed of: 
Oxide of lead 27.31 
Resin 72.69 
100.00 
This same combination, analyzed with oxide of copper, gave 
precisely the same composition as that of resin of copaiba and 
the crystallised resin of colophane. 
General Observations on the Jicid Resins. — It follows, 
from the preceding experiments, that the resins produced by 
the oxidation of the essential oils are not only isomeric, but also 
that they have the same capacity of saturation as regards bases. 
MM. Blanchet and Sell have found that the isomeric essential 
oils, which are not oxigenized, combine with hydrochloric 
acid, sometimes in one proportion, sometimes in another. 
If the above mentioned resins be considered as acids, they 
differ from most of those of organic origin, by the absence of 
water of crystallisation; as it is well known that hitherto but 
few of the organic acids have been obtained in an anhydrous 
state, except by combining them with bases. Unverdorben, 
it is true, considers sylvic acid as a hydrate, but this opinion 
is contradicted by the experiments of M. Rose. 
All the combinations of the acid resins with bases examined 
by this chemist, are also destitute of water of crystallisation; 
after having washed them with alcohol, they dry readily, and 
do not attract moisture from the air. 
The change of essential oils into resins has often been com- 
pared to that of fatty bodies into acids, but the experiments of 
M. Rose show the fallacy of this comparison; doubtless by 
the oxidation of fatty substances in the air a small quantity of 
acid is generated, but there is also a formation of other pro- 
ducts; whilst the transformation of the essential oils into resins 
is a simple result of the oxygenation of the oil by the oxygen 
of the atmosphere. 
Resins which do not possess the properties of Jicids. — 
M. Rose treats only of a few of the crystalline resins of this 
