332 REPORT— 1886. 



Such being the case, it becomes very necessary, in the determination of the 

 conductivity of electrolytes, to take account of the character of the electrodes, 

 and at the same time the above observation would point to the fact that with 

 pure metallic surfaces the effect of contact resistance is constant, if it occurs at all. 



Again to fiu-ther test this point, the absolute value of a certain copper sulphate 

 solution was determined by employing two distinct cells. 



(1) Cell A, the tube of this cell had a length of 31*4 cm., its mean section 

 being 10-66 square cm. 



The copper sulphate solution placed in this cell gave a resistance value of 

 .504-5 legal ohms at 18-1°. 



(2) Cell B, the tube of this cell had a length of 24-16 cm. and a mean section 

 of 13-21 square centimetres. 



The copper sulphate solution placed in this cell gave the value 306-9 legal 

 ohms at 18°. 



The same platinum electrodes were used in both cases. 



The values obtained for the resistance of a cubic centimetre of the copper sul- 

 phate solution differed by about 2 per cent. 



The values being, with cell A 



11 = 171-2 legal ohms. 

 With cell B 



11 = 167-8 legal ohms. 



These results woidd again tend to show that there is no effect due to contact 

 resistance. 



Another point, which seemed of importance, was the action of the solvent in the 

 conductivity of electrolytes ; and, with the view of experimenting on this subject, 

 solutions were prepared containing the same salt, whilst the solvents were different. 



In the first place equal quantities of copper sulphate were dissolved in distilled 

 water and in glycerine, the resistance of the two solvents having been previously 

 determined. 



(1) The resistance of 500 cm. of water introduced into the cell gave a resist- 

 ance of R = 12,780 legal ohms ; in this water was dissolved 6-625 gms. of hydrated 

 copper sulphate ; the resistance value was now R = 8-87 legal ohms at 17-2°. 



(2) The glycerine, which was not pure, gave the value 



R= 181,000 legal ohms. 



In this was dissolved 6*625 gms. of hydrated copper sulphate, and the resulting 

 value was 



R = 27,850 at 16-8°, 



From these results the conductivity of a solution would appear to a large extent, 

 and in fact mainly, to depend on the solvent employed. The comparison of solu- 

 tions of copper sulphate in water and glycerine was not, however, continued, as 

 there appears to be some slight chemical action whereby a very small quantity of 

 copper oxide is precipitated ; and hence it was thought that this would not be 

 allowed perhaps to be a case of solution similar to that of the copper sulphate iu 

 water. 



The case, however, of solutions of calcium chloride in water and absolute 

 alcohol appeared to be iu every way comparable, as a definite crystalline compound 

 of calciimi chloride and alcohol exists similar to the hydrated crystalline chloride. 

 For this purpose equal quantities (i of a gramme-equivalent) of pure anhydrous 

 calcium chloride were dissolved in 500 ccm. of water, and also in 500 cc. of 

 absolute alcohol (sp. gr. -795), the resistance of the alcohol and also of the water 

 having been previously determined. Then by dilution solutions were prepared of 

 250 cc, containing ^^, i, ^, &c., of a gramme-equivalent of the salt in 500 cc. of 

 the solvent. 



Two series of values were thus obtained for solutions of different dilutions in 

 both alcohol and water, wherein we can compare the action of the two solvents.' 



' In each case 250 ccm. of solution was introduced into the cell. 



