[ARCHIBALD] CONDUCTIVITY OF AQUEOUS SOLUTIONS 71 



Preparation and Analysis op Simple Solutions. 



The method udopted was to mtike up as eoncentrated a solution as I 

 wished to measux'e. This solution was carefully analysed, and from this 

 successive multiple dilutions were prepared by adding water, all solu- 

 tions being })repared at a temperature of 18° < '. 50 c.c. of these solutions 

 would be introduced into the electrolytic cell, and successive dilutions pre- 

 pared from this in the cell itself, by withdrawal of a certain volume and 

 addition of an equal volume of water. As a check upon errors in dilut- 

 ing, after a portion had gone through a certain number of dilutions, it 

 was taken from the cell and carefully analysed, and if found necessary 

 the previous determinations of the concentration were corrected from 

 the data thus obtained. 



In these analyses the concentration of the potassium and sodium 

 chloride solutions was determined volumetrically. A solution of silver 

 nitrate standardized at 18°C. was used to estimate the chlorine, neutral 

 potassium chromate being used as indicator. To test the accuracy of this 

 mode of analysis, two solutions of sodium chloride were prepared contain- 

 ing known quantities of the pure fused salt. These were analysed by the 

 above method and results found to be correct to O'l percent. In the case 

 of the potassium and sodium sulphate solutions the concentration was 

 determined gravimetrically, the quantity of salt in solution being 

 estimated from the amount of barium sulphate precipitated by barium 

 chloride when added in slight excess to a known volume of the solution 

 to be analysed. Four determinations of one solution by this method 

 gave a possible error of 0-15 per cent. 



All pipettes and burettes used were calibrated by weighing the water 

 they delivered. No pipette was used in which the time of outflow was 

 less than forty seconds. The point of the pipette was allowed to rest 

 against the side of the vessel during the outflow, and when it had ceased 

 the pipette was blown into without removing the point. 



Preparation of the Mixtures. 



Curves were drawn on co-ordinate paper, showing the relation of 

 dilution ( F) to concentration of ions (a/Y) for solutions of each of the 

 four salts. A common concentration of ions was then selected and the 

 dilution for each salt corresponding to this value of a/Y taken oflT its 

 curve. This gives the dilutions of the solutions to be mixed. The volumes 

 to be mixed, that the dissociation of each electrolyte might not change on 

 mixing, were then calculated as shown above. 



Where fractions of one c.c. had to be measured out, a pipette was 

 used the neck of which had been calibrated by weighing the water deliv- 



