Diffusion of Hydrogen through Hot Platinum. 13 
In a recent paper*, one of the authors has treated the 
problem of a dissociating gas diffusing in solution, and in the 
one-dimensional case has arrived at the following expression 
for the number N of gramme-molecules of gas per second 
diffusing through a slab of solvent of thickness d: 
eh ea i }; Xo” 
eis d iE (aE rtm ps | 
where n is the number of submolecules produced by the 
dissociation of each molecule : 
fn, #= coefficients of diffusion of the dissociated and undis- 
sociated gas molecules, respectively: 
kj=the dissociation constant outside and &, inside the 
solution ; 
1/A is the partition coefficient of the undissociated gas, and 
A, is a real root of the equation of dissociation 
Cy” + hycg=hyPo, 
where P, is the total concentration of the external gas and c, 
is the partial concentration of the dissociated molecules. All 
the concentrations are molecular. 
Since in the present experiments we are dealing with flow 
through the walls of an annular cylinder, we ought not to 
use the one-dimensional solution. It is, however, just as easy 
to obtain the solution for this case. In the paper cited, it is 
shown that the concentrations satisfy the equation : 
2 en ie 
V(u0+ 0) =0, 
where C, ¢c are the concentrations of the undissociated and 
dissociated gas respectively. Since everything is a function 
of x only V7” becomes 
Zo 
| dr. + 
The conditions to be fulfilled are: at the external boundary 
{r=r,) C=c=0, and at the internal boundary (r=?) 
a 
dr° 
vy Hn Cy, Ma % 
BC+ pie as a’ 
C,, €) being the values of © and ¢ outside, and 1/a the 
partition coefficient of the dissociated gas. The necessary 
* Phil. Mag. [6] vol. vii. p. 266. 
