of the Molecular Structure of the Hydrocarbon Compounds. 95 
equation we can put r=q=v,=v,=14,570 and v,=0. If also 
we put 2v=a, Vv, +X, V+, V5, (H,, X,, ©, representing respect- 
ively the number of single, double and treble carbon bonds 
which occur in the molecule of the hydrocarbon in question), 
we can write equation (17) in the following more convenient 
form : 
(C,, H,,)=—2X 38,900°+- (2m-+a,--e,) 14,570° (18) 
This formula may be readily adapted to the various types of 
hydrocarbons (the paraffines, the olefines, the acetylenes, benzol, 
ete.), and by its aid we can calculate the heat of formation of 
different isomers according to their assumed structure, and then 
on comparing the calculated values with the direct results of 
experiment we may hope to obtain a new test of our theories 
of molecular structure. 
n the series of paraffines the carbon atoms are all linked by 
single bonds, and no isomerism resulting from different rela- 
tions of the carbon bonds is possible. Of course isomerism can 
result from differences in the grouping of the carbon atoms, 
but of this our thermo-chemical theory takes, as yet, no 
account. The general formula of a paraffine is C, H,,,, and 
2m=2n+2; z,=n—1; x,=0. Making these substitutions in 
(C,, Hyp 4.) =X 4810°+414570° (19) 
and the caleulated values of the heat of formation under con- 
stant volume for the first three members of the series is as 
follows. The observed values in the parallel column shows as 
close accordance as could be expected. 
TaBLE VII. 
Calculated. Observed. 
, 19,380° 19,570¢ 
O.Hs 24,190° 24,510° 
C;Hs 29,000° 39,950°¢ 
In the olefines, however, isomerism resulting from different 
relations of the carbon bonds is possible; thus in the case of 
C,H, we may have 
c 
CaF a, ae eee 
Pee aoe 
The general formula of an olefine being C,H,,, we have in 
the first case n single carbon bonds, and in the second case 
n—2 single bonds together with one double bond. Making 
the obvious substitutions in equation (18), we have for the heat 
of formation under constant volume 
(1) (Ca, Hoa) = n x 4810° 
(2) (Cu, Hog) = m x 4810° — 14,570¢ 
