OF CERTAIN ORGANIC ACIDS IN AQUEOUS SOLUTIONS. 51 



PROCEDURE. 



The cell constants were taken by the method described by White and 

 Jones. 1 When working at low temperatures they were determined as 

 often as once a month, and still more frequently when working at high 

 temperatures. The experimental difficulties are much more numerous 

 at the higher than at the lower temperatures. There is a greater and 

 more frequent variation in the cell constants. The solubility of the 

 glass is often too large to be negligible. A few short quotations from 

 the work of Clover and Jones, referred to above, will give the results 

 of their investigations in the best possible forms. 



CELL CONSTANTS. 



"It has developed that a strain is brought about by the high temperatures 

 which may result in a change either in the distance of the electrode plates from 

 each other or in the surface of the plates. Since such a variation had not 

 previously been observed in work covering a range of to 35, it was thought 

 that the changes might be reduced by maintaining the cells at a temperature 

 which was about a mean of those employed in the experimental work. Accord- 

 ingly, when not in use, the cells were filled with pure water and placed in a 

 bath which was maintained continuously at a temperature of 45 to 50." 



They performed an experiment to test the value of this method. 



"The measurements were first carefully made at 35 and then duplicated; 

 then the regular systematic procedure was gone through at 65, and after this 

 the readings at 35 were again made. If the results found the second time 

 should agree with those first obtained at 35, this would be strong evidence 

 that the method was reliable. It was found in some cases that the second 

 reading differed slightly from the first. In other cases there was no difference, 

 and the change appeared to be independent of the cell used, or the concen- 

 tration of the solution. It was further found that on standing for a con- 

 siderable length of time at 35 (2 or 3 hours), the reading slowly changed back 

 in all cases to the original value. It is difficult to see what other causes can be 

 assigned to these results than a temporary change in the cell constant during 

 the heating at 65." 



In conductivity work carried out at ordinary temperatures, experi- 

 ments have shown that the error introduced by the solubility of 

 the glass is negligible. However, at 50 the error from this same source 

 at a dilution of one liter is the largest of all the ordinary experimental 

 errors. The glass is still more soluble at 65, as would be expected. 

 Clover and Jones point out that at 80 the conductivity of pure water 

 is increased tenfold on standing in the cells for a couple of hours. The 

 cells used in their research were made of hard glass. Obviously, the 

 amount of glass dissolved from the cells depends largely upon the nature 

 of the glass of which the cells are made. It varies considerably with 

 the different cells. The attempt to introduce directly a correction 

 factor for the solubility of glass was therefore abandoned. This source 

 of error was overcome in another way. 



. Chem. Journ., 42, 520 (1909). 



