COMMUNICATION TO THE EDITOR
1132
largely by the transition of the crystal structure. The author wishes to express his thanks to Pro-
Vol. 61
fessor Ryutaro Tsuchida for his kind guidance and encouragement throughout this work.
COMMUNICATION TO THE EDITOR I
THERMODYNAMIC RELATION BETWEEN osition that "no matter what two systems for ACTIVITY COEFFICIENTS OF HYDRATED describing concentration are involved AND UNHYDRATED SOLUTE ala, = a'/a', (2) where a denotes activity and * refers to another Sir: By two equally rigorous methods, welt2 have obtained the correct relation between activity coefficients calculated on the conventional unhydrated basis and on the basis of a hydrated solute. This relation is In
y =
1ny
- Z1n aw - In [I - 0.018(n - u)m]
composition." This undoubtedly is true for different systems of describing the concentration of the same component, e.g., the well-known relation between the activity coefficients of an unhydrated electrolyte on mole-fraction and molarity scales
+ 0.018m)
f = -/(l (1)
and it rests on incontrovertible thermodynamic proof. Miller3now asserts that the term n/v In a, should not appear. The basis of his argument is the prop(1) R. H. Stokes and R. A. Robinson, J . Am. Cham.Soc., TO, 1870 (1948). (2) R. A. Robinson and R. H. Stokes, "Eleotrolyte Solutions," Butterworths Publications, London, 1955. (3) D. G . Miller, THIS JOURNAL, 60, 1296 (1956).
But it cannot hold if one concentration is the molality of an unhgdrated solute and the other is the mole fraction of hydrated solute. DEPARTMENT OF CHEMISTRY THEUNIVERSITY OF NEWENQLAND N.S.W. R. H. STOKES ARMIDALE, AUSTRALIA OF CHEMISTRY DEPARTMENT UNIVERSITY OF MALAYA R. A. ROBINSON SINGAPORE RECEIVED DECEMBER 11, 1956
*
P
