Dissociation of Compounds in Water. 481 



but is considerable for the more concentrated. After the 

 four most concentrated solutions had been measured, which 

 required several hours, the solution was titrated against 

 standard acid, and found to have lost about ^ per cent, of the 

 calculated concentration. This error increased rapidly with 

 increase in concentration, and prevented the use of more 

 concentrated solutions than those which were employed. 



Potassium Carbonate. — The carbonate is slightly more dis- 

 sociated than the sulphate. The carbon dioxide was also 

 removed from the water used in preparing the solutions of 

 the carbonates to prevent the formation of acid carbonates. 

 The solutions of the carbonates must have also been slightly 

 affected by the carbon dioxide of the air. The hydrolysis of 

 the carbonate molecules into KOH and KHC0 3 by the water 

 in dilute solution, and the subsequent dissociation of these 

 products of hydrolysis, would give slightly too great lowerings 

 of the freezing-point and consequently a dissociation somewhat 

 too high. 



Sodium Carbonate. — Three compounds of potassium and 

 sodium have then been investigated — the chlorides, hydroxides, 

 and carbonates. The chlorides dissociate to the same degree, 

 ■within the limit of error ; the hydroxides to very nearly the 

 same extent ; sodium hydroxide possibly a little less in the 

 more concentrated solutions. The carbonates have about the 

 same dissociation in the most dilute solutions, but the differ- 

 ence noticed with the hydroxides increases here. Sodium 

 carbonate dissociates less with increased concentration, and 

 this difference amounts to 4 per cent, at 0*1 n. 



Comparison with Kohlrausch's Results from 

 Conductivity. 



The Conductivity method is probably the most exact 

 hitherto employed for determining dissociation. It admits of 

 wide application, and has the advantage over the Freezing- 

 point method that it can be applied to more dilute solutions. 

 It will suffice to compare a few of the results obtained by the 

 two methods. 



Most of the compounds discussed thus far in this communi- 

 cation have been studied by Kohlrausch*, as to their conduc- 

 tivity, with that care which characterizes his work. He has 

 employed equivalent-normal solutions throughout, while I 

 have used gram-molecular normal, Where the two do not 

 coincide, Kohlrausch's results have been reduced to molecular 

 normal and compared directly with mine. This applies to 



* Kohlrausch, Wied. Ann. xxvi. p. 160. 

 Phil. Mag. S. 5. Vol. 36. No. 223. Dec. 1893. 2 K 



