( 185 ) 
Bw In fig. 1 AD and BD are the lines fiving 
7 a graphic representation of the change of a as 
5 function of the ratio of the ions J/, and 
B WM, at a constant total concentration of the 
cations. A point on AD, therefore, gives 
the concentration of the M, and M, ions in 
an electrolyte, which is in equilibrium with 
A 
M, and the potential difference at the plane 
A JZ, of separation between this electrolyte and the 
electrode. BD does the same for M. Both 
~ °My-ions. lines are logarithmic curves. AD, therefore, 
asymptotically approaches the ordinate M/,B, until it is intersected in 
D by the line LD. 
In D the electrolyte is in equilibrium with the two metals J/, and 
M,. To the left of it, M, is precipitated by M,, to its right, M, by 
M,. The condition of equilibrium in D is a, = a, 
1 Py 1 Pr 
therefore log — = — log — 
n 1 P 1 n 2 Ps 
ny Pi Ny Pr 
or oe Noe aes 
Pa Ps 
and, for metals of the same valency P: Piz = p, : py. 
In words: in this equilibrium the ratio of the concentrations of the 
cations is equal to the ratio of the solution tensions of the metals. 
Owing to the great difference in the solution tensions, p, must 
in most cases be very small and consequently the possibility of the 
second metal existing in contact with the mixed electrolyte, is limited 
to very minute concentrations of the first metallic salt; whereas the 
first metal may be in equilibrium with almost all the electrolytes, 
whatever the proportions of the two salts may be. The point D 
is, therefore, situated nearest to the less noble metal and almost 
coincides with B. 
DanNEEL *) has investigated an instance of this equilibrium, namely 
2HI + 2 Ag=@2 AgI+H,. The solution, which is in equilibrium 
with both Ag and H, under 1 atm. pressure, is saturated with Agl 
(c = 0,567X10—-8) and 0,043 normal in HI. 
Il. The two metals form a homogeneous liquid or solid solution. 
This is the case with the liquid amalgams and other fused metals, 
with Zn—Ag ®), Sb—Sn ’*) and other alloys. 
1) Z. f. Phys. Ch. 33, 415. 
2) Heycock en Nevittr. J. Chem. Soc. 1897, 415. 
5) Heycock en Nevitte. J. Chem. Soc. 330, 387; van Burerr, Z. f. phys. Ch, 
8, 357 en Reinpers Z. f. anorg. Ch. 25, 113. 
