384 
MR. JOHNSTON ON THE CONSTITUTION OF THE RESINS. 
varieties of the dragon’s blood of commerce. But my remarks on the resin of benzoin 
have extended so much, that I think it better to reserve them for a future opportunity ; 
I may merely state generally, that while the formula assigned to the resin contained in 
the lump dragon’s blood is C 40 H 21 O g , and to the drop variety after long heating at 
300° Fahr, C 40 H 20 0 8 , the same varieties yield by the action of quicklime and of 
oxide of lead, among other products two resins, represented approximately by C 40 
O 10 , and C 40 H 20 0 12 ? ; that the resin of assafoetida, which in Part IV. is expressed by 
C 40 H 26 O 10 , gives with oxide of lead one resin, C 40 H 23 0 13 ; that the resin of jalap 
— — C 4 q H 3 4 0 18 , in like manner with oxide of lead, gives a new resin, C 4 q H 34 O 20 , and 
the resin of guiacum C 40 H 23 O 10 , one represented by the formula C 40 H 21 O n . The 
experiments from which these and other interesting formulae are deduced, I shall have 
the honour of laying before the Society on a future occasion. 
Having in the former papers on this subject, and in the commencement of the pre- 
sent, established certain approximate irrational formulae for numerous resins, we have 
by these later results and observations been led considerably further in advance, and 
into a new portion of the field of inquiry. 
They have opened up the question as to the rational constitution of the resins, and 
have enabled us to hazard a conjecture, in regard to what that constitution may really 
be. 
We have seen reason from the irrational constitution of the resins to divide them 
into two groups characterized by unlike general formulae, and we have observed a 
general analogy also in physical characters, among the members of each group. A 
comparison of the effect of bases on these several resins seems to confirm the propriety 
of this division, since the analyses of the salts of the resins, of which colophony is the 
type, appear to show that in combining with bases they undergo no change, or if any, 
only in regard to the number of atoms of hydrogen, and this is doubtful ; while all 
those resins, to the salts of which reference has been made in the present paper, in- 
dicate an important metamorphosis or decomposition as the result of the action of 
bases. This distinction, if general, is a very wide one, and must arise from the ar- 
rangement of the constituent elements in twm ways very unlike each other. Too 
much weight, however, is not to be attached to these apparent distinctions, as they 
may vanish on further investigation. 
Durham , June 3, 1840. 
