MR. JOHNSTON ON THE CONSTITUTION OF THE RESINS. 
353 
5. A fifth portion after long- heating at 212°, owing to the drying of the water-bath, 
was allowed to remain for sometime at a higher temperature. Its colour was in some 
degree darker. 
7’36 grs. gave C = 17"67, and H = 4*50 grs. 
These results give per cent, respectively, 
1 . 
At 21 2° for a short time. 
2. 
12 hours at 180° and 
1 hour at 212°. 
3. 
2 hours at 212°. 
4. 
Fused at 250°. 
5. 
Half an hour at 
250° ±. 
Carbon 63"21 
64'15 
64-01 
64-90 
66-38 
Hydrogen 6'66 
6'66 
6-75 
6-66 
6-79 
Oxygen 30' 13 
29'19 
29-24 
28-44 
26-83 
100 
100 
100 
100 
100 
From the mode in which these several specimens of resin were prepared, it is ob- 
vious that Nos. 2 and 3 represent most nearly the normal state of the resin. In No. 
1 so much of the volatile matter remained as to prevent the resin from entirely con- 
creting ; while in 4 and 5 the heat had been raised, or prolonged, so as to cause par- 
tial decomposition. The formula C 40 H 25 0 14 , gives 
Per cent. 
40 Carbon = 3057-480 64' 15 
25 Hydrogen = 31T99 6*52 
14 Oxygen = 1400-000 29*33 
4769-47 100 
which agrees very closely with the results of the second and third analyses, while 
those of the first and fourth analyses oscillate on either side of the calculated num- 
bers. We seem to be justified therefore in adopting this formula for the constitution 
of the resin of opoponax, as it exists in the natural gum resin of commerce. 
In reference to the analyses 4 and 5 above given, I would draw attention to a fact 
which may hereafter prove of considerable consequence when we come to consider 
the rational constitution of the resins. It will be observed that, by an increase of 
temperature, sufficient to produce partial decomposition, the carbon increases, while 
the per centage of oxygen decreases almost in equal proportion, that of the hydrogen 
remaining nearly constant. This was the case also as above shown with the resin of 
retin-asphalt, and approximately also with that of ammoniac, and we shall have occa- 
sion to make the same remark in regard to several other resins to be treated of in 
the following sections. I may mention, especially that of assafoetida, with the ana- 
lysis of which I propose to conclude the present part of these researches. 
The nature of this action of an elevated temperature is shown more clearly by 
mdcccxl. 2 z 
