52 CONDUCTIVITIES AND DISSOCIATIONS 



It was found that after the cells had been heated with water for 

 several hours, the amount of glass dissolved gradually decreased and 

 finally became practically nothing. After this treatment, as the cells 

 were kept in a bath at 45 and 65 and the water in them changed once 

 a day, the solubility of the glass at 65 was always practically zero and 

 therefore negligible. If a cell was removed from the bath and allowed 

 to stand filled with water at room temperature for any appreciable 

 length of time, it was found on heating that glass was again dissolved. 



In this investigation the above precautions were all observed. In 

 addition, at the start of the work the glass vessels were heated with 

 a dilute solution of caustic soda, then boiled with dilute hydrochloric 

 acid, and then for some time with conductivity water. The solubility 

 of the glass was shown by tests to have been reduced to a negligible 

 quantity by this treatment. The cells were then kept filled with con- 

 ductivity water which was changed every day, and were maintained 

 at a temperature approximately 50, and thus the solubility of the glass 

 was negligible. This was proved experimentally. A cell was filled 

 with conductivity water at 35 and the conductivity read; then it was 

 heated and readings were made at both 50 and 65. The solution was 

 cooled to 35 and the conductivity again measured. Since the two 

 readings at 35 coincided, there was no appreciable quantity of glass 

 dissolved during the process. 



This was not the only beneficial result obtained from keeping the 

 cells always at an elevated temperature. The expansion of glass and 

 of platinum is not large enough to affect appreciably the cell constants, 

 as would be the case if the temperature varied over a wider range. 



It has already been stated that it takes several hours for a cell to 

 acquire its normal condition at the lower temperature, with respect to 

 the electrode-plates and the glass rods when suddenly cooled. This 

 fact was utilized in the determination of the cell constants at the higher 

 temperatures. The cells were kept at about 50, and when the cell 

 constants were to be taken the cells were filled with the solution of 

 potassium chloride and they were heated to 50 for about an hour. 

 The cells containing the solution were then cooled down and the con- 

 ductivity read immediately after a constant temperature had been 

 reached. The readings were made at 25, where the conductivity of 

 the solutions of potassium chloride is accurately known. 



The method of White and Jones was used for taking the cell con- 

 stants over the entire range of temperature from to 65. 



Two objects w r ere accomplished in all the work at higher tempera- 

 tures, by filling the cells nearly to the top with the solutions. First, 

 evaporation and the consequent change in concentration were reduced 

 to a minimum. Second, carbon dioxide and other gases from the air 

 were prevented from being present in sufficient quantity to affect 

 the results. 



