ELECTRICAL CONDUCTIVITIES, ETC. 7 



higher temperatures a strain seemed to develop in the cells unless they were kept at 

 a fairly uniform temperature. This resulted in a small change in the cell constants, 

 due either to a change in the distance between the plates or in the surfaces of the 

 plates themselves. Errors would be introduced, especially in the case of those cells 

 whose plates were close together which had small cell constants. 



Since such a variation as that referred to above had not previously been observed 

 over the temperature range to 35, it was thought that the changes in the cell 

 might be reduced to a minimum by keeping the cells at a temperature which was 

 about the mean of those employed in the experimental work. Accordingly, the 

 cells, when not in use, were rilled with pure water and placed in a bath which was 

 maintained continuously at a temperature of from 45 to 50. 



To test the accuracy of the procedure adopted the following experiments were 

 carried out. The conductivities of several different substances at the three dilu- 

 tions, 5, 1024, and 2048 liters were measured in the cells ordinarily used for solutions 

 of these concentrations. The measurements were first carefully made at 35, then 

 the solutions warmed to 65 and their conductivities determined. The solutions 

 were then cooled down to 35 and their conductivities redetermined. If the con- 

 ductivities found the second time at 35 agreed with those initially found at this 

 temperature, it would be some evidence as to the reliability of the method used. 

 In about half the cases the two sets of measurements at 35 agreed very satisfactorily , 

 In the other half, the second readings differed slightly from the first, and the differ- 

 ence seemed to be independent of the cell employed or the concentration of the 

 solution used. 



In all of those cases where any difference was detected between the initial and 

 final conductivities at 35, this difference always disappeared entirely on allowing 

 the cells to stand at 35 for two or three hours. This showed that any slight change 

 that the cell might have undergone at the higher temperature disappeared when the 

 cell was kept for a time at the lower temperature. 



SOLUBILITY OF GLASS. 



In conductivity work at ordinary temperatures this factor has always been neg- 

 lected and probably is not sufficiently large to influence the results, even with very 

 dilute solutions. However, at 50 the error introduced by this factor at a dilution 

 of 1000 is greater than any of the other ordinary experimental errors. At 65 the 

 solubility of the glass is still greater, and at 80 the conductivity of pure water is 

 increased tenfold on remaining in the cell for a couple of hours. In this connection 

 it may be stated that the cells employed were made of hard glass. Of course, the 

 amount of glass dissolved depends upon the exact nature of the latter, and was found 

 to vary considerably with the different cells used, and at different intervals in the 

 case of any one cell. The idea of introducing a correction for the solubility of the 

 glass was abandoned, but the difficulty was overcome in another way. It was 

 found that after the cells had been heated with water, acid, and alkali for several 

 days, the amount of glass dissolved gradually decreased and finally amounted to 

 practically nothing. After this treatment, as the cells were kept in a bath at 45 

 to 50 and the water in them changed once a day, the solubility of the glass at 65 



