MR. JOHNSTON ON THE CONSTITUTION OF THE RESINS. 
381 
]our of a resin is a consequence of incipient decomposition, and is almost always at- 
tended by the evolution of a volatile oil. 
2. Dilute solutions of carbonate of soda in the cold readily dissolve crystallized 
benzoic acid ; but trituration, or even boiling with such solutions, does not deprive 
benzoin of the power of yielding this acid when subjected to heat. Concentrated solu- 
tions of the carbonated alkalies by boiling produce this effect, but they may act on 
the elements of the supposed oil as caustic potash does. 
3. When boiled with caustic lime we have seen that a new resin is produced con- 
taining much more hydrogen ; the same effect follows, and to a greater extent, by 
treatment with caustic potash even in the cold. This effect is most readily explained 
by supposing a decomposition to have taken place, by which a substance containing 
less hydrogen (benzoic acid) is separated, and one containing more is formed, or se- 
parated along with it. 
4. It may be stated, as in some measure corroborating the above arguments, that 
when the resin of dragon’s blood is heated for a length of time at a temperature at 
which it barely fuses, it gives off benzoic acid, water, and a reddish volatile oil, but 
is at the same time itself so much decomposed, that though retaining its red colour 
it becomes in a great measure insoluble in alcohol. 
These reasons do not appear to me to decide that no benzoic acid exists in the 
benzoin resin of commerce, but they render it probable, I think, that very little does 
so exist, at least in a free state , in the white varieties. The brown varieties appear 
to be already in some measure decomposed, and hence their colour, and the presence 
probably of some free acid ; but all the varieties undergo further decomposition and 
yield more acid, when exposed to a high temperature or to the action of bases, which 
by their affinities dispose the elements to arrange themselves so as to liberate benzoic 
acid. 
But admitting this explanation, the question remains, In what state do the ele- 
ments of benzoic acid exist in the resin ? Is benzoic acid present as such, but in com- 
bination with the resins, which by the action of alkalies and oxides are eliminated 
along with it ? Are the resins analogous to the fatty bodies, and do the bases act upon 
each family of substances in an analogous manner, liberating from the former an oil, 
the analogue of glycerine (hydrated oxide of glyceryle = C 6 H 7 O s + H O) and two 
resins, the analogues of the oleic and stearic acids ; and is this oil again, by a secondary 
action of the bases, converted into benzoic or some similar acid, and one or more other 
as yet undetected compounds ? Or do the resins consist of this or an analogous acid 
ready formed and directly combined with one or more basic resins ? Though I feel 
shown, however, that no other substance is formed at the same time as the benzoic acid. Berz. Arsberattelse, 
1837, p. 269. 
It is interesting to observe, that in C 20 H u 0 2 , or C 40 H 22 0 4 , we have the same ratio of the carbon to the 
hydrogen as in our resin C 40 H 22 0 9 . 
