of the Molecular Structure of the Hydrocarbon Compounds. 91 
calculation, combining the several values according to the prin- 
ciple of least squares. This Thomsen has done, and deduced 
for the most probable values 
a=106,630°. r=14,573. 
With these values it is now easy to calculate the following table: 
TABLE IIT. 
Symbol. Heat of Formation. Differences. 
ba Es ee iar ee ed 
HC=CH —a+ 4r= — 48,338° tr = 102,011 
H.C=—CH, —a+ r=— 4,619¢ Qr = 131,157 
H,C—CH; —a+ = 14,637 oe 1 45,730 
H,C | CH, —a+10r= 39,100¢ 
and by comparing these calculated values with the observed 
values of table II it will be seen how closely they satisfy the 
observations. In table III the,value —a is the heat of forma- 
tion of the assumed product C=C from amorphous charcoal, 
and is the sum of two quantities, first the amount of heat 
absorbed in completely disassociating the atoms from the amor- 
phous solid coal, and secondly the amount of heat that must 
be set free in the union of free carbon atoms in pairs by four 
nds. If now we represent the first value by —2d and the 
second as already proposed by v, we can evidently make the 
equation 
—a= -2d+v, =—106,630°. (1) 
If a hydrocarbon is formed from amorphous carbon and hy- 
drogen gas, the process must involve in addition to the disas- 
sociation of the atoms of the coal a division of the molecules 
HC=CH=(C,, H)=—2d+0,$2ch-hh. (2) 
It will be noticed that the symbols in lower case type are used 
represent what we have called the thermal potentials of the 
atoms. 
_ Assuming, as the facts of organic chemistry undoubtedly 
Justify, that the thermal effect in the union of hydrogen and 
on atoms is always the same, and putting ~ 
