TO THEIR STATE OF IONIZATION MACGREGOR. 231 



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 case of his first mixture calculated above, the difference 

 amounts to only 0.0 3 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 differ- 

 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 isohydric. i. 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 isohydric 

 the condition of its vanishing will be 



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, &c. 



The conclusions drawn by Bender and Bruckner 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. 



