96 J. Thomsen’s Thermochemical Investigation 
For propylene n =8, and the calculated values are +14,480° 
or —150°. According to Thomsen’s experiments the heat of 
formation of propylene prepared from isopropyliodide is —400°, 
which would indicate that the generally received opinion in 
regard to the structure of this molecule is correct. 
With the acetylenes we may have three distinct types of 
structure depending on the distribution of the carbon bonds. 
Thus for C,H, either 
ee or =C=—0= or —C=0—C— 
met eens eee | 
The general symbol for an acetylene being C, ee 
we have in isomers of the first type n—1 single with one 
double bond ; in isomers of second type n—8 single with two 
double bonds, and in isomers of the third type n—2 single 
with one treble bond. Making the substitutions as before, we 
obtain the following equations : 
(1) (Ca, Hon — 2) = n. 4810° — 29140° 
(2) (Ca, Hon — 2) =. 4810° — 43710° 
(3) (Ca, Hon —- 2) = m. 4810° — 58280° 
and for allylene the three values are 
—14710° —292838°  ~43856° 
A determination of the heat of combustion of allylene was 
with the generally received opinion. The discrepancy between 
theory and observation, however, is quite large, and Thomsen 
intends to make further experiments on this substance. 
One feature of this investigation of Thomsen, which might 
be overlooked unless attention was called to it, may be appro- 
priately noticed in this connection. Omitting the unknown 
quantity x, which indeed is probably zero, we have for the 
values of the carbon bonds, 
=f t= Fr 0 0 0=—2r 
ee eee ee eee Se ir vee ee Ne ne Sa 
