( 450 ) 
may be compared, as has been observed by Drupr and REINGANUM '), 
to a value of the same expression that is obtained from other data. 
I shall suppose that the charge e of an electron is equal to that of 
an ion of hydrogen in an electrolytic solution and I shall represent 
by p the pressure that would be exerted, at the temperature 7, by 
gaseous hydrogen, if a unit of volume contained one electrochemical 
equivalent. Then 
al 
— =p. 
The proof of this formula is as follows. We may write for the 
: ; 1 
number of atoms in unit volume of the gas considered — for the 
e 
1 
number of molecules =, and, since the mean kinetic energy of a 
ze 
rp 
. Asis well 
molecule amounts to «7, for the total kinetic energy 
ae 
known, the numerical value of the pressure per unit area is two 
thirds of this. 
Using the C.G.5. system and electromagnetic units, we have for 
the electrochemical equivalent of hydrogen 0,000104 and, putting, 
T = 273° + 18°, 
op == 38. 
On the other hand, the measurements of JanGeR and DrrsseLHORST 
have given for silver at 18° C. 
ke 
Den Gyiskr << TOE, 
whence, by (29), 
al 
— = 47. 
e 
The agreement between the results of the two calculations, for 
which the data have been furnished by widely different phenomena, 
though not quite satisfactory, is close enough to make us feel con- 
fident that Drupr’s theory rests on a sound basis”). 
§ 10. We might now return to the formula (25) and, denoting 
by @ the electric potential, so that 
1) Remeanum, Theoretische Bestimmung des Verhältnisses von Wärme- und 
Elektrizitätsleitung der Metalle aus der Drupe’schen Elektronentheorie, Ann. Phys., 
2 (1900), p. 398. 
2) A better agreement is found if, instead of (28), we use Drupe’'s formula. 
