the Solvent in Electrolytic Conduction, 387 



the aqueous solutions, they have a very considerable conduc- 

 tivity. 



In all cases the water solutions conduct best, though the 

 conductivity of the water itself is much smaller than that of 

 the methyl-alcohol. 



It should be mentioned that in the table of results the con- 

 ductivity of the solvent has in all cases been subtracted, and 

 the tabulated results are the difference between the observed 

 values of the conductivity of the solvent and of the saline 

 solution ; that this is legitimate is clearly shown by the results 

 obtained by Prof. Kohlrausch for the conductivities of solu- 

 tions of the same strength in water of varying conductivity. 

 It has been before mentioned that the character of the salt, as 

 well as of the solvent, influences the conductivity of the solu- 

 tion ; and I conclude that there is an interaction between the 

 two, on the result of which interaction the conductivity chiefly 

 depends ; this would be the formation of molecular groups in 

 the solution. 



That such molecular groups do exist in solution in certain 

 cases experiment clearly proves. 



Prof. Kohlrausch, in determining the conductivity of solu- 

 tions of sulphur trioxide in water, found that, for certain 

 strengths of solutions, the conductivity was a minimum ; 

 namely, those that corresponded to the proportions S0 3 . H 2 0, 

 and S0 3 . 2H 2 ; on further dilution the conductivity again 

 increased. In these particular cases, the solution was com- 

 posed of these molecular groups. 



Again, the work of Arrhenius on isohydric solutions shows 

 that, if solutions of two compounds of different strength be 

 mixed, the conductivity of the resulting solution is the mean 

 of those of the two. A molecule of the first body thus reacts 

 with a different number of molecules of the solvent from that 

 with which a molecule of the second reacts, and the two mole- 

 cular groups can exist in solution without affecting one another. 



Certain salts form compounds called cryohydrates, winch 

 separate out from solution at very low temperatures ; that 

 such compounds exist in the solution previously to separating 

 out in the solid form must be admitted. Quite recently, in 

 experimenting with solutions of sodium chloride, with a view 

 to the determination of ternperature-coefhcients at low tempe- 

 ratures, I found that of two solutions, the first of which was 

 saturated, whilst the other had a specific gravity of 1 # 052, 

 when cooled down in a freezing-mixture to —19° C, the 

 saturated solution behaved regularly, the conductivity falling 

 with the fall of temperature. For the more dilute solution 

 this was not the case ; at — 7° the solution began to solidify, 



