TO THEIR STATE OF IONIZATION—-MACGREGOR. Za 
however, with the aid of the constants for surface-tension deter- 
mined above, we compute, in the case of Sodium and Potassium 
Chlorides, the difference between the value for a mixture and 
the volume-mean of the values for its constituents, we find it 
to be beyond the limit of Rother’s power of observation. Thus, 
in the ease of his first mixture calculated above, the difference 
amounts to only 0.0,15. His conclusion should thus have been 
that the difference, if any, between the surface-tension of a 
mixture and the volume-mean of those of its constituents was 
within the limits of his experimental error. He might even 
have concluded, however, that there was probably such a difter- 
ence in the case of Sodium and Potassium Chlorides ; for in all 
the mixtures of solutions of these salts which he examined, the 
volume-mean of the values for the constituent solutions were 
found to be less than the values for the mixtures. 
The above expression (5) will vanish if the constituents of 
the mixture are isohydrie, 2. e., have states of ionization which 
do not change in the mixing; and it will vanish in that case, 
whatever the values of the other quantities involved in the 
expression may be. When the constituents are not isohydri¢ 
the condition of its vanishing will be 
My (lg—Kg)(@o'—Ge)¥g Dr tiie (6) 
Me, (ly —ky) (4, —24')v4 
It is obviously improbable that in any case in which this con- 
dition may be fulfilled the numbers of gramme-equivalents per 
litre in the constituent solutions will have a simple relation, 
such as 1:2, 4: 3, & 
The conclusions drawn by Bender and Brickner from their 
observations on density, thermal expansion, electrical conduc- 
tivity, and viscosity, viz., that there is such a simple relation in 
the case of all “ corresponding” solutions, so far as the proper- 
ties mentioned are concerned, is thus inconsistent with the possi- 
bility of expressing the values of these properties in terms of 
the state of ionization. 
