io6 



Conductivity of Aqueous Solutions. Part IV. 



In the cases of the two tri-ionic salts the apparently abnormal phenom- 

 enon is observed that their equivalent conductance, though about equal to 

 or less than that of potassium chloride at 18, becomes much larger than it 

 at the higher temperatures. The very large values of the ratios at 281 and 

 306, especially for potassium sulphate, can not be caused by hydrolysis ; 

 for this would have an opposite effect, owing to the smaller equivalent 

 conductance of the univalent ions thereby produced (for example, of the 

 OH - + HS0 4 ~ ions which would replace the S0 4 - ion) : and at the lower 

 temperatures (218 and below) appreciable hydrolysis does not exist, since 

 the acids and bases involved have been shown by the measurements of 

 Noyes and Eastman (section 97, Part VIII) to be too much ionized to 

 admit of it. The real peculiarity in the results does not, however, con- 

 sist in the large value of the ratio at the higher temperatures, but rather 

 in the approximation of it to unity at the lower ones; for, since a 

 bivalent ion, like Ba ++ or S0 4 = , is in the same electric field, owing to 

 its double charge, acted on by twice as large a force as a univalent ion, 

 it would, provided it met with the same resistance, move with twice the 

 velocity, and therefore have twice the equivalent conductance. The equiv- 

 alent conductance of a completely ionized uni-bivalent salt would therefore 

 approach 1.5 times that of a uni-univalent salt if the specific velocities of 

 the various ions (that is, the velocities under unit electric force) 

 approached equality. An approximation to this limiting value seems to be 

 indicated in the case of potassium sulphate, and a change in the same 

 direction is clearly shown by barium nitrate. That the equivalent conduct- 

 ances of the bivalent ions are so small at ordinary temperatures signifies, 

 of course, a high resistance to their passage through the solution. This 

 may arise from their being much hydrated ; and the large increase in 

 velocity with rising temperature may be due to a decrease in the hydration. 



In order to show more clearly the relation between equivalent conduct- 

 ance and temperature for the individual substances, we have calculated 

 the values of AA /A for the successive temperature intervals, and tabu- 

 lated them in table 26, together with those for potassium and sodium 

 chlorides already given in section 18, Part II. 



Table 26. Temperature-coefficients of the equivalent conductance at zero 



concentration. 



