1023 
molecules, and bear in mind that in HI and H, the vibration of 
the atoms at ordinary temperature does not yet manifest itself in 
the amount of the specific heats, but that this 7s the case for iodine, 
(see § 6), so that the term of vibration of the iodine molecule will 
be the predominating one, then with neglect of the r-terms for 
HI and H,, equation 15 may be transformed into: . 
MM, ZnEro ; ie | 
En ann -==log K + log\ 1—e FT) + 2.263 . (20) 
ABTT 
If we now fill in the value 15u for 4, (see § 6), the observations 
of STRGMÜLLER (gas cells)') and of Bopenstri (direct dissociation 
determinations) *) yield the following table: (p. 1024) 
If equation 20 is written in the form: 
M,M Sn Tro 
aen EN Te d 
°F 4.571 
log 
(21) 
in which C represents the value of the second member of 20, every 
time multiplied by the corresponding absolute temperature, then ina 
graphical representation, in which C is laid out as function of 77, 
the observations must forma straight line. Then it appears graphically 
that a straight line can be drawn through the observations with the 
MM, nr : 
— = 1,184 and ED 529; the observed points 
4 
are then spread on both sides of this line. Then follows for the 
expression of the iodine hydrogen equilibrium: 
parameters /og 
972 
529 OT 
ieee dee le MRE 
It will certainly be possible to make a slight modification in the 
parameters without appreciably impairing the agreement between 
calculated and found values; it appears from the subjoined table 
that the errors in the observations at the lowest temperatures are 
pretty large, but that the expression 22 satisfactorily represents the 
other observations. 
Dissociation determinations at high temperatures have been made 
by Voer, von FaArCKENSTEIN®). They have been carried out by 
measurement of the partial pressure of the hydrogen, use being 
made of the permeability of platinum to this gas, and of its imper- 
meability to the other gases. The equilibrium constants, which have 
1) SrEGMÜLLER. Zeitschr. f. Elektrochem. 16. 85 (1910). 
2) BoDeNsTEIN. Zeitschr. f. physik. Chem. 29, 295 (1899). 
8) loc. cit. 
