The lonisation of Dilute Solutions at the Freezing Point. 197 



In the case of copper sulphate, measurements by the present method 

 ■were made at 18° as well as at 0°, and are indicated by crosses inside 

 circles ; giving a curve which agrees with Kohlrausch's observations at 

 moderate concentrations, but differs from them at extreme dilution. 



The normal type of curve is given by potassium chloride, barium 

 chloride, &c. The curve for sulphuric acid departs from this form, as 

 other observers, using glass vessels and working at higher tempera- 

 tures, have previously found. The drop in this curve at extreme 

 dilution is seen also in solutions of other acids and alkalies, and it has 

 been usual to explain it by supposing that the effective amount of acid 

 is reduced at extreme dilution by interaction with the residual im- 

 purities of the solvent. The phenomenon seems too constant for this 



Table I. 



JHoSOi = 49-04, Solvent. Weight = 219-42, E = 40420. 





m. 



mi. 



E. 



K/m. 



a. 





3 -254 X 10-5 



0-0319 



3106 



9-122 



0-809 



II 



9-628 „ 



0-0459 



954-3 



10-62 



0-941 



Ill 



2 -001 X 10-4 



-0585 





11 -10 



0-984 



IV 



3 -558 



-0709 



247 -8 



11 -26 



0-999 





6-340 „ 



-0859 



139 



11 -26 



0-998 





1 -425 X 10-3 



0-1125 



63-11 



11 -09 



0-984 



VII 



2-411 „ 



-1341 



37 -75 



10-90 



0-967 



VIII 



3 -423 „ 



0-1507 



27-25 



10-73 



0-951 





4 -729 „ 



0-1678 



20-05 



10-53 



0-934 





In Glass Cell. 









I 



3 '660 X 10-3 



0-1541 



1789 



-1552 



0-948 





5-381 „ 



1752 



1246 



-1516 



0-926 



Ill 



1 -158 X 10-2 



-2262 



615-7 



-1426 



0-871 



IV 



1 -747 „ 



-2595 



424-4 



-1347 



0-837 



explanation to be satisfactory, and the cause of it may perhaps be con- 

 nected in some way with the fact that it occurs only in solutions the 

 solute of which gives ions either of hydrogen or hydroxyl, which are 

 ions (1) present in the solvent, (2) possessing greater velocities than 

 any other ions. 



The drop in the ciu-ve for potassium permanganate is, on the other 

 hand, probably due to interaction between the salt and the solvent 

 impurities. The effect is completed by the first addition of salt, for if 

 a correction be made in the case of the first solution for the salt thus 

 put out of action, it is found that the curve reverts to the normal 

 type. This is clearly shown by the diagram. Again, both in this case 

 and in that of sulphuric acid, it was foTincl that for solutions of great 

 dilution the resistance showed a gradual rise for some time after the 



VOL. LXVI. R 



