DILUTE SOLUTIONS AT THE FREEZING POINT. 3'25 



valuable saving of time which would otherwise have been lost in cooling each solution 

 after it had been diluted and returned to the cell. 



It had at first been intended to transfer each solution from the freezing point 

 apparatus to that in which the resistance was to be measured, or rice versd, so that 

 experiments for the determination of both constants might be made on identical 

 solutions. This could not be done if a series of solutions was made up in either 

 apparatus itself. But the advantage to be obtained is not so great as at first sight 

 appears, since it is unwise to move dilute solutions through air, or to cool them more 

 often than necessary. Moreover, by using water prepared in the same way for each 

 series of experiments, and adding stock solution by similar methods, it seemed that 

 strictly comparable results would be obtained. 



SECTION 2. On the Electrolytic Cell. 



Having settled, then, that the solutions were to be prepared separately in the 

 two sets of apparatus, it remained to devise a cell to contain the liquids while their 

 resistances were being measured. 



It seemed likely that some of the discrepancies between the results of different 

 measurements of freezing points might be due to the action of glass dissolved from 

 the containing vessel. It was therefore decided to carry out the freezing point work 

 in platinum vessels only, and to preserve both the water used and the solutions from 

 all contact with glass. Similar precautions were therefore taken in the resistance 

 measurements. 



The following conditions had to be satisfied in the design of the apparatus : 



1. The cell itself and all parts which might by any means touch the liquids con- 

 tained in it must be of platinum. 



2. There must be two insulated platinum electrodes, rigidly fixed relatively to each 

 other. Since the vessel was to be made of a conducting substance, it was evident 

 that its walls must be used as one of the electrodes. 



3. Small changes in the level of the liquid must not appreciably affect the 

 electrical constant of the cell. 



4. The temperature of the vessel and its contents must be under easy and efficient 

 control. 



5. Means of emptying and filling the cell must be provided, and also of adding 

 stock solution to the cell when in position. 



6. Stirring apparatus must be arranged to secure uniform temperature, and to mix 

 the stock solution when added with the former contents of the cell. 



After many alterations and one complete reconstruction, the apparatus assumed 

 the form shown in section (fig. 1). 



The walls (a) of the platinum vessel are used as one electrode, a platinum cage (6) 

 suspended near its centre, forms the other. This cage, consisting of a short hollow 



