370 
MR. JOHNSTON ON THE CONSTITUTION OF THE RESINS. 
cally stated. The investigation of this resin indeed has presented many difficulties, 
chiefly, as it appears to me, from the ease with which it undergoes a partial decompo- 
sition even at very moderate temperatures. I have made numerous analyses of it, in 
various states, with the view, if possible, of establishing a formula for it in the normal 
state, and, amid the many changes it undergoes, of arriving at a process by which it 
may always be obtained of uniform composition. How far this end has been attained 
the following experiments will show. 
The resin of benzoin, as it occurs in commerce, consists of brown opake brittle 
masses, containing here and there small pieces of a yellowish white colour and semi- 
transparent. These latter portions melt at about 200° Fahr. into a transparent nearly 
colourless resin, which on cooling becomes brittle. At a higher temperature it gives 
off water and benzoic acid, and becomes brown. 
1. Of this pure white variety a portion was dissolved in alcohol, evaporated and 
heated in a thin film at 212° Fahr. till it ceased sensibly to evolve benzoic acid. 
During this heating it gradually assumed a brownish tinge. In this state, when burned 
in the air, it left 0*29 per cent, of ash. 
7'64 grs. (7*618 grs. pure resin) gave C = 19*60, and H = 6*84 grs. 
2. The colourless resin in its natural state, without being dissolved, was kept for 
twenty hours in a semifused state at 200° Fahr. It left, when burned in the air, 0*24 
per cent, of ash, and 
9*87 grs. (9*847 grs. pure resin) gave C = 26 grs., and H = 5*907 grs. 
3. The same natural resin was dissolved in alcohol, evaporated, subsequently treated 
with repeated portions of boiling water, which dissolved out benzoic acid, and then 
dried at 212° Fahr. It left 0*23 per cent, of ash, and 
8*21 grs. (8*192 grs. pure resin) gave C = 21*76, and H = 5*23 grs. 
4. The natural mixture of brown and white resins was boiled repeatedly in water, 
twice with dilute solutions of carbonate of soda, with the view of extracting all the 
benzoic acid, and again in water to separate the soda. It was then dissolved in al- 
cohol, evaporated and dried at 212° Fahr. It left 0*3 per cent, of ash. 
11*46 (11*426 grs. pure resin) gave C = 29*73, and II = 7*363 grs. 
5. A portion of the resin thus treated (4.) was again boiled in a concentrated solu- 
tion of carbonate of potash, washed with a dilute solution of muriatic acid, and after- 
wards boiled in acetic acid and well washed with water. It still retained some potash, 
for when burned in the air it left 1*03 per cent, of ash, being 0*73 of carbonate of 
potash, and the usual 0*3 per cent, of earthy matter. This quantity of carbonate of 
potash retained 0*26 per cent, of carbonic acid, the potash and earthy matter being 
together 0*77 per cent. The resin was of a reddish-brown colour, and was soluble 
without residue in both alcohol and ether, though, according to Unverdorben*, 
boiling with carbonate of potash converts benzoin into two resins, one soluble and 
* Thomson’s Organic Chemistry (1838), p. 542. 
