Diffusion of Hydrogen through Hot Platinum. 23 
that Q should vary with 6 very approximately as k,. Now 
the way in which £, varies with the temperature can easily be 
obtained. It is given by the equation * 
LOSE Vis Sai 4, 
ee am, aw 
where g, is the heat of dissociation of hydrogen when the 
dissociation takes place inside platinum, and v’ is the change 
of volume when 1 gm.-molecule of hydrogen dissociates 
completely at pressure p. Expressing, q, in small calories, 
pv’=R=2 7 very approximately, so that we may write the 
equation 
d(lozk,) — g 1 p 
ey el a ee (9) 
whence k?=CO2e 
oo ee aa (6) 
Da UG 40 
We have seen that the number of gramme-molecules which 
flow through unit area per second is given by 
where Pis the numberof gramme-molecules per c.c.of hydrogen 
at O° C. under the pressure 7 (in cms. of mercury) observed 
during the experiments. To reduce to the mass Q per sq. cm. 
per sec., we have to multiply by the molecular weight of 
hydrogen (2), and by the factor 7°68 x10-* to reduce to 
pressure readings. We then get 
77m 1 
A 722 3 M2 k, a 1 
()=7°68 x 10 x x (3) TT 
. che oe one 
or since d=‘01 em. in the experiments, 
Gy ula: oe cal i 
= 15 (4) st ett ie orteay GE) 
Hliminating &, between (6) and (7) we obtain :— 
C . : : : 
logyo re a logy,Q— 2 1og100 ++ = — logyo7? + shy. (8) 
The quantity on the right-hand side is thus seen to be a 
* See for instance J. J. van Laar, Arch. Néerl. [ii.} v. p. 490. 
+: Van’t Hoff, ‘ Lectures on Theoretical Chemistry,’ vol. i. p. 21, 
