50 CONDUCTIVITIES AND DISSOCIATIONS 



The thermometers employed were carefully compared with a stan- 

 dard Reichsanstalt thermometer. The standard thermometer was also 

 calibrated at the United States Bureau of Standards. 



The resistance box which was used throughout this entire investiga- 

 tion had also been calibrated by the Bureau of Standards. A very 

 fine slide wire bridge was employed, the wire being wrapped around a 

 marble drum. On this bridge the investigator could easily read to 

 fractions of a millimeter. The entire scale was 5 meters long, and read- 

 ings could be made to tenths of a millimeter. 



The cells were kept at a constant temperature in thermostats. As this 

 work was carried on simultaneously with that of Dr. Wightman, and 

 partly using his apparatus, reference is made to his description of the 

 system of thermal regulation. In the paper by Wightman and Jones 1 

 the system of regulation for temperatures to 35 is fully described. 

 They say: 



"Three thermostats were employed to keep the cells at constant tempera- 

 ture; one for similar to that described by Jones and Jacobson; 2 one for 15 

 (in this case for 12.5) and 25, a galvanized tub containing 20 to 30 liters of 

 water, and in the bottom of which was placed a lead (in this investigation, 

 copper) coil through which cold water was passed under constant pressure; 

 a third for 35, differing from the latter only in not having a coil in the bottom. 

 They were both kept constantly stirred by propellers driven by a hot-air 

 engine. In this way it was possible to keep the temperature constant to 

 within 0.02." 



The work at the more elevated temperatures was carried out in 

 apparatus similar to that used at the lower temperature, with the 

 difference that the thermostats were covered with asbestos boards 

 saturated with paraffin. The thermometer and stirrer passed through 

 small openings in the cover, and the cells were placed in the bath 

 through openings just large enough to admit them. These holes were 

 covered by pieces of the same material as the cover. The evaporation 

 of the water in the bath was in this way reduced to a minimum, and 

 the confined vapors maintained the cells, both the exposed portion and 

 the part immersed in the bath, at the same temperature. Thermo- 

 regulators of the same type as are used throughout this laboratory were 

 employed. 



There has been much less work done here at higher than at lower 

 temperatures; therefore, a more detailed description of the various 

 difficulties encountered, and the methods devised to overcome them, 

 will be given. 



The only work that had been previously carried out at the higher 

 temperatures is that of Clover and Jones 3 and of West and Jones. 4 



r. Chem. Journ., 46, 56 (1911). 3 Ibid., 43, 187 (1910). 



*Ibid., 40, 355 (1908). *Ibid., 44, 508 (1911). 



