358 
MR. JOHNSTON ON THE CONSTITUTION OF THE RESINS. 
General Remarks. 
At the close of the former Part (III.) of these researches, I stated that a slight 
change in the general formulae we had seen reason to adopt, as representations of the 
constitution of the resins, would be rendered necessary by certain analyses which I 
had already made, but which were not in a state for publication. Some of these ana- 
lyses are contained in the present paper, and I shall here shortly advert to the modi- 
fications they suggest. 
I. As a general expression for all the resins of which the composition was then 
known, I proposed the irrational formula C 40 in which x varied from 
0 to 12, and y from 1 to 12. No resins were then known which had been shown with 
any degree of certainty to contain more than thirty-two of hydrogen to forty of 
carbon. 
II. Observing also that those resins in which the hydrogen was less than twenty- 
four atoms possessed physical and chemical properties analogous to each other, yet 
remarkably distinct from those exhibited by the resins in which the hydrogen ap- 
proached to thirty-two atoms, I was induced to subdivide the resins into two sec- 
tions, represented respectively by 
C 40 H 32 - x of which colophony is to be regarded as the type ; and 
C 40 H 24 _ x O y , of which gamboge and dragon’s blood are members. 
III. In the present paper, however, are introduced three resins, those of scammonv 
(C 40 H 33 O 20 ), jalap (C 40 H 34 0 18 ) and labdanum (C 40 H 33 0 7 ), in which the hydrogen 
exceeds thirty-two atoms. To include these, therefore, our first sectional formula 
must be modified by the insertion of the plus ( + ) after 32, giving it the form 
C 40 H 3 2 ~tx 0'/3 
in which state it includes the three resins above-mentioned, in which the hydrogen is 
present in greater quantity. 
It may, perhaps, become a question hereafter whether these resins ought not to be 
placed in a separate section, represented by C 40 H 32+<r O y , since their properties, 
and especially their action upon the system, is so very different from that of any of 
the resins of the pine tribes, of which colophony is the type. This point, however, 
will become more clear after the other resins usually classed by systematic writers 
along with those of scammony and jalap have been examined and analysed. 
In connexion with this alteration in our formula deduced from the analyses above 
given, I ought to advert to two formulae for the crystallized resin of elemi, lately 
published by Professors Hess of Petersburgh and H. Rose of Berlin*. The former 
chemist assigns to this resin the formula C 40 H 33 O, and the latter C 40 H 34 O, differing 
only in regard to the presence or absence of one atom of hydrogen. Whichever of 
these formulae be adopted, the change above introduced into our general expression 
* See Poggendorff’s Annalen, vol. xxxiii. p. 51 ; vol. xlvi. p. 322 ; vol. xlvii. p. 61 ; vol. xlix. p. 219. 
