342 
MR. JOHNSTON ON THE CONSTITUTION OF THE RESINS. 
oxygen than the resin itself. Nearly all the resins when heated to incipient decom- 
position give off more or less of a volatile oil, bat in general the per centage of carbon 
is increased by such decomposition. 
This resin is remarkable for containing the largest quantity of oxygen of any resin 
hitherto analysed. In this respect it exceeds even the resin of jalap, to which, as the 
subsequent section shows, it has so much analogy in constitution, and which it re- 
sembles also in its action on the system, and in the genus of plants ( convolvolus ) from 
which it is derived. 
X. Resin of Jalap. 
The resin of jalap is stated by chemical writers, chiefly, I believe, on the authority of 
Cadet de Gassicourt*, to consist of two resins, of which only one is soluble in ether, 
though both are extracted from the root by alcohol. In this statement, however, 
there is an error, the source of which will presently appear. 
I was induced to turn my attention to this resin in connection with that of Scam- 
mony, of which the analysis is above given, in consequence of a statement of Gobel 
that this resin contains more oxygen than any other. He found it to consist of car- 
bon 36’62, hydrogen 9’4 7, and oxygen 53*91 This result, however, is very wide of 
the truth, and though jalap resin does contain a large per centage of oxygen, it is in- 
ferior in this respect to the resin of scammony. 
I. The jalap resin of the shops, in lumps of a dark green colour, when digested in 
ether, gives a dark brown solution, and with the exception of a small quantity of im- 
purities, dissolves entirely. When evaporated, this solution yields a brown resin, 
emitting, while fused, the distinct and nearly unmixed odour of common colophony. 
As I had every reason to believe that in this state it is largely adulterated, I did not 
subject the resin thus obtained to any further examination. 
II. An ounce of powdered jalap was digested in alcohol, the brown solution evapo- 
rated to dryness, and the dry resinous mass treated with ether. A considerable por- 
tion of the mass was taken up by the ether, and alcohol dissolved nearly all that was 
left. This agrees with the statement of Gassicourt, who says that of the resin ob- 
tained by evaporating the alcoholic solution, ether dissolves -^ths, leaving undissolved 
a second resin to the amount of -j^ths of the entire weight. 
III. As the purity of powdered jalap is not to be depended upon, half a pound of 
the roots was sliced and digested in cold alcohol of the shops, for three weeks, and 
the solution evaporated.. A dark brown mass was obtained, which, after heating to 
150° Fahr. for several days, refused to dry up and harden. It presented the ap- 
pearance, and when warm had the consistence and something of the smell of treacle. 
It had also a sweetish taste mixed with that of jalap, and when set aside in the cold 
speedily began to deliquesce. 
This mass was treated with boiling water, which dissolved at least two-thirds of 
* Handbuch der Chemie, von Leopold Gmelin, ii. p. 569, and Thomson’s Organic Chemistry, p. 540. 
t Dr. Todd Thomson’s Materia Medica, ii. p. 290, 1833. 
