jj<5 Conductivity of Aqueous Solutions. Part XII. 



The results given under A (S)/A (kcd in table 139 show that the 

 values of the equivalent conductance for complete ionization in the case 

 of all the di-ionic substances investigated become more nearly equal as 

 the temperature rises, the approach toward equality being rapid between 

 18 and 218, but comparatively slow at the higher temperatures. This 

 shows, of course, that the specific migration-velocities of the ions are 

 themselves more nearly equal, the higher the temperature. Complete 

 equality has not, however, been reached even at 306, but the divergence 

 exceeds 5 per cent only in the cases of hydrochloric acid, sodium hydrox- 

 ide, and sodium acetate, which have ions which at 18 move with excep- 

 tionally large or small velocities. 



The behavior of the tri-ionic salts, potassium sulphate and barium 

 nitrate, is especially noteworthy. Their equivalent conductance increases 

 steadily with rising temperature and attains values which are much 

 greater than those for any di-ionic uni-univalent salt. Thus at 306 the 

 value for potassium sulphate is about 1.5 times as great as that for potas- 

 sium chloride. This behavior, which at first sight appears abnormal, is in 

 reality in conformity with the principle that the velocities of ions sub- 

 jected to the same electric force approach equality with rising tempera- 

 ture ; for, assuming that the resistance of the medium becomes the same 

 for all ions, the velocity of a bivalent ion, owing to its double electric 

 charge, should become twice as great as that of a univalent ion under 

 the same potential-gradient ; and correspondingly, the equivalent con- 

 ductance of a completely ionized uuibivalent salt should become 1.5 times 

 that of a completely ionized uni-univalent salt. What is remarkable is, 

 therefore, not the greater values at high temperatures, but the approxi- 

 mate equality at room temperature of the equivalent conductances of 

 bivalent and univalent ions, especially of the elementary ones which might 

 be expected to have not far from the same size. This equality may be 

 due, as has been suggested by Morgan and Kanolt,* to a relatively large 

 hydration of the bivalent ions. 



With respect to the form of the temperature-conductance curve, it 

 will be seen from an examination of the values of AA /Af that the rate 

 of increase of conductance is in case of all the neutral di-ionic salts greater 

 between 100 and 156 than it is between 18 and 100 or between 156 

 and 218, f and therefore that the curve is first convex, later concave, and 

 then again convex toward the temperature axis, with two intermediate 

 points of inflexion. 



In the case of the acids and bases, however, and therefore of the hydro- 

 gen-ion and the hydroxide-ion, the rate of increase of the equivalent 



*J. Am. Chem. Soc, 28. 572 (1906). 



fWith respect to this last temperatu re-interval sodium acetate forms an exception. 



