92 J. Thomsen’s Thermochemical Investigation 
2ch — hh=2q* (3) 
we can readily deduce for the several hydrocarbons we are 
studying the following equations: 
TABLE IV. 
For, - G0 —a = — 2d + v4. 
HC=CH —at+ 4r= — 2d + v5 + 2 
H,.C=CH, —a+ Ir= — 2d + v, + 4¢ 
H;C—CH, —a+ 9=—%Wd+n, + 6g 
H,C.1CH, —¢@+10r= —2¢d....+8 
and from the differences between the successive equations of 
this group we obtain the following simple relations between 
the quantities we are investigating : 
V4 —V3 = 2g — 4r 
=2q— r 
It will be seen that we have’thus madea very near approach 
to the determination of the thermal value of the several bonds 
between the carbon atoms, but as in the last group the num- 
ber of unknown quantities exceeds by one the number of sep- 
arate equations (it must be remembered that r is known), we 
must look for some other relation to furnish an additional con- 
dition. We'can find this, in part at least, in the thermal rela- 
tions of the oxides of carbon. 
The heat of formation of the oxides of carbon from amor- 
phous carbon and oxygen gas, and also the heat of formation 
of carbonic dioxide from carbonic oxide and oxygen gas are 
given in the following table: 
TABLE V. 
Heat of Formation 
Under constant pressure. Under constant 
(C, Ox) 6,960° 96,960¢ 
(CO O) 68,370¢ 68,080¢ 
The first of these values is the same as that used above, de- 
termined by Favre and Silbermann. The second has recently 
en re-determined by Thomsen. The third is not an experl- 
mental value, but deduced by simply subtracting the second 
from the first. As there is no condensation of gas volume 
when oxygen gas passes into carbonic dioxide, the heat of for- 
mation of carbonic dioxide under constant volume is the same 
as that under constant pressure. But when carbonic oxide gas 
unites with oxygen gas to form carbonic dioxide there 1s 4 
condensation of one half a molecular volume, and hence in this 
case the value under constant volume is less than that under 
* Notice that the quantity q is the result of two processes necessarily sumulta- 
neous, the breaking up of the hydrogen molecule and the union of the hydrogen 
and carbon atoms. oe ae 
