226 
SELECTED ARTICLES. 
question, which especially applies to the art of prescribing, 
have examined comparatively the two resins. They have 
determined that if the resin of the Convolvulus Orizabensis 
resembles in some points that of the officinal jalap, it differs 
from it in others; which analogies and differences can be sum- 
med up in a few words under the two following heads: 
Properties common to the two Resins — Properties peculiar 
to each of them. 
The properties common to the two resins are — 
1. Their solubility in alcohol. 
2. Their solubility in cold nitric acid . without the extrication 
of deutoxide of azote. 
3. Their color; although, in strictness, this character should 
be of little value, the decoloration taking place without the 
resin being in other respects affected. 
The properties peculiar to the resin of the new jalap 
are — 
1. A sweetish, slightly nauseous taste. 
2. Solubility in ether. 
3. Suspension in water without an intermediate sub- 
stance. 
Those peculiar to the resin of the old jalap are— 
1. An acrid, irritating, persistent taste. 
2. Insolubility in ether. 
3. Agglutination in water, even when cold. 
It follows from this comparison that, in the pharmacological 
classification of the resins of the convolvulacese, that of the 
new jalap should form the type of a new genus, intermediate 
between two others, one of which comprehends the resin of the 
Convolvulus officinalis, the other that of the Convolvulus 
scammonia. 
We have, moreover, found in the new jalap both nitrate of 
potassa, and a substance which becomes green upon exposure to 
the atmosphere. It is insipid, insoluble in cold water, partially 
soluble in boiling water, insoluble in absolute alcohol and in 
ether, either cold or hot. This substance is obtained by precipi- 
