348 
MR. JOHNSTON ON THE CONSTITUTION OF THE RESINS. 
3. In order to ascertain the effect of a still more protracted heating, a further por- 
tion of the solution was evaporated in a thin film, and kept at 200° Fahr. for sixteen 
hours. The heating appeared in this instance to have produced incipient decompo- 
sition, the resin having acquired a slightly darker colour than the portions previously 
analysed. 
In this state 6*865 grs. (6*852 grs. pure resin) gave C = 18*4, and H = 5*81 grs. 
The three results above obtained give respectively, 
1 . 
12 hours at 150°. 
2. 
20 hours at 200°. 
3. 
16 hours at 220°? 
C40 H 31 O, gives 
C 4 o H 3o 0 7 gives 
Carbon 73' 1 6 
73-98 
74-25 
73*63 
74-00 
Hydrogen 9 '43 
9-39 
9-42 
9-33 
9-06 
Oxygen 17 ‘41 
16-63 
16-33 
17-04 
16-94 
100 
100 
100 
100 
100 
From the appearances presented during the prolonged heating, I am inclined to 
consider the resin of 2 to have been nearly in the normal state, and that the portion 
3 had been heated too long. The chief difficulty is in regard to the hydrogen, as 
considerable pains were taken in exhausting the moisture from the combustion tube. 
Considering, however, the comparatively low temperature at which the exhaustion 
must be performed, in order to prevent loss, in the case of a resin which melts so 
easily as the present, I am inclined to adopt the formula containing H 30 as the safer 
of the two. 
There is still therefore a relation between the Berengela and labdanum resins, the 
former being represented by C 40 H 30 0 7 , and the latter by C 40 H 33 0 7 . 
XIII. Resin of Retin- Asphalt. 
Having thus succeeded in bringing the Berengela resin within the dominion of our 
general formula containing C 40 , 1 became desirous of ascertaining how far my present 
experience of the mode of obtaining the several resins in the normal state, might 
enable me to deduce for the resin of Retin-Asphalt a formula which would be in- 
cluded in the same general expression. 
This resin is extracted by alcohol or ether from the mineral retin-asphalt of Bovey, 
of which it constitutes about sixty per cent. Evaporated at 212° the solution affords 
a light brown unfused resin, which begins to melt at 250° Fahr., is fluid at 300°, and 
at a temperature not exceeding that at which it becomes fluid, gradually decomposes. 
It is sparingly soluble in cold alcohol, more largely in boiling alcohol, from which it 
is partially precipitated on cooling. Ether dissolves it more easily and in greater 
quantity, giving a dark brown solution. 
On a former occasion I published * two analyses of this resin, from which I deduced 
the formula C 21 H 14 0 3 . Into this formula the constant C 40 does not enter, as the 
analyses were made before the commencement of the present investigation had taught 
* London and Edinburgh Journal of Science, Third Series, vol. xii. p. 561. 
