( 778 ) 
Physics. — “On “osmotic temperatures” and the kinetic signification 
of the thermodynamic potential.’ By Prof. Pa. Kounstam. 
(Communicated by Prof. J. D. van per Waars). 
(Communicated in the meeting of December 24, 1910). 
1. It may be presumed to be known, at least in Holland, how 
easily the laws of the diluted solutions are derived from the general 
differential equation of vaN per Waars for coexisting phases: 
PI 0°¢ 
VP = a dT + («,— (ar) eid en Ka 
The law for the osmotic pressure alone does not immediately 
follow from the equation in the above form for the simple reason 
that it has been supposed in the derivation of this equation that the 
pressure in the two coexisting phases is equal. If we, however, return 
to the derivation of equation (1), we see at once the relation between 
this equation and the law of van ’r Horr. This derivation, namely, 
runs as follows. As in two coexisting phases 1 and 2 the thermo- 
dynamic potential e.g. of the first substance must be equal, and also 
in two other coexisting phases 1’ and 2’, the change of this thermo- 
dynamic potential between 1 and 1’, and 2 and 2’ must also be the 
same, and so if we take 1 and 1’ near each other, and represent 
the molecular thermodynamic potential of the first substance as 
usual by «,, the equation : 
[d By], = [d ul. 
5 0c 
is == 
m1 = da pr 
dz ds 
dg =de da —ad 
’ Ow vT Oar pl 
; ] Ds 
dS =vdp — 74dT + | — |de 
a pl 
and 
(2) = (le (PE r+ OTE 
we get: 
holds. 
Now from: 
follows 
\ 
And 
