MR. JOHNSTON ON THE CONSTITUTION OF THE RESINS. 
371 
the other insoluble in ether. This change, however, I am satisfied must, in Unver- 
dorben’s experiment, have proceeded from some other cause than simple boiling in 
carbonate of potash. It may possibly have been due to the action of caustic alkali 
contained in his carbonate, which, as I shall hereafter have occasion to show, exer- 
cises an important modifying power over this resin at a boiling temperature, convert- 
ing it into at least two resins of very different composition ; or the manner of heating, 
or length of time during which it was boiled, may have led him to a result different 
from that which I have obtained. In the case of substances so susceptible of meta- 
morphoses, as the resins will hereafter appear to be, we ought to hesitate in ascribing 
to errors of observation, a difference in results which may have arisen only from a 
slight difference in the circumstances under which the experiments, made by different 
chemists, were conducted. The benefit of this observation is especially due to Un- 
verdorben, who did so much, considering the state of chemistry in his time, to throw 
light on this interesting family of organic products. 
Thus boiled in carbonate of potash, 
A. 8*945 grs. (8*8/6 grs. pure resin) gave C = 23*22, and H = 5*95 grs. 
B. 9*905 grs. (9*829 grs. pure resin) gave C = 25*905, and H = 6*66 grs. 
The entire results above-detailed, allowing for the earthy matter and for the car- 
bonate of potash, present in these last, give per cent., 
Dissolved in alcohol and 
heated to 21 2° Fahr. 
Native resin heated 
long at 200° Fahr. 
Dissolved in alcohol 
and treated with 
boiling water. 
Boiled in water and 
in dilute carbonate 
of soda. 
Boiled in concentrated 
carbonate of potash. 
A. 
B. 
1 . 
2. 
3. 
4. 
5. 
6. 
Carbon 71' 14 
73-06 
73-43 
7195 
72-59 
7313 
Hydrogen 6"84 
6-67 
7-09 
7-16 
7-45 
7-53 
Oxygen 22-02 
20-27 
19-48 
20-89 
19-96 
19-34 
100 
100 
100 
100 
100 
100 
These results are very discordant, and on such of them as have not been repeated, 
perhaps much reliance ought not to be placed. There is so far an agreement among 
them, however, that the per centage of hydrogen goes on increasing with every suc- 
cessive operation to which the resin is subjected. This is quite in accordance with what 
ought to take place, if we suppose that additional portions of benzoic acid are re- 
moved at each step. Anhydrous benzoic acid consists of C 14 H 5 0 3 , or calculated to 
C 40 , for the purpose of comparison, it is C 40 H 14 . 3 0 8 . 57 . In this latter formula, while 
the oxygen is slightly in excess, the hydrogen is many atoms less than in the resin 
in any of its states. The extraction of benzoic acid from the resin, must therefore 
necessarily increase the proportion of hydrogen in what remains, while, with the aid 
of the water evolved at the same time, the oxygen will be to a certain extent dimi- 
nished. The resin analysed after boiling in dilute carbonate of soda (4.) still gave off 
benzoic acid and water, when heated in a close tube, while after further boiling in 
concentrated carbonate of potash it gave no sensible quantity of crystals (analyses 
3 b 2 
