of the Molecular Structure of the Hydrocarbon Compounds. 89 
seeks to determine the thermal value of these several bonds 
determined (Pogg. Ann., v. , 390), are united in the column 
under I in the following table. Under column II of the same 
sen), the heat of combustion both of amorphous carbon and of 
hydrogen gas, namely, 
(C, 0,)=96,960°  (H,, 0)=68,360° 
it is very easy to calculate the values in column II from those 
in column I; for by a well-known principle of thermo-chemis- 
try the heat of formation of a hydrocarbon is equal to the dif- 
ference between the heat of combustion of the compound and 
sum of the similar values for the charcoal and hydrogen gas 
from which it is assumed to be formed. In the case of CH,, 
20,150°=96,960°+-2 X 68,360° — 213,530°, 
mean temperature of 20° C. 580° are set free for every molecu- 
lar volume lost by condensation. In the formation of CH, from 
4H, one molecular volume is lost, and hence by subtractin 
580° from 20,150° we obtain the amount of heat which woul 
ave been evolved had the product occupied the same volume 
as the factors from which it was formed. In like manner the 
