72 



Conductivity of Aqueous Solutions. Part IV. 



Fig. 17. 



0.70 cm. in diameter and 0.35 cm. in height resting upon a vertical quartz 

 cylinder 1.40 cm. in height, as illustrated in fig. 17. 



This electrode and cylinder were afterwards replaced by a quartz cup, 

 1.42 cm. in diameter and 1.52 cm. in height, which formed "cell in." The 

 electrode was 1.34 cm. in diameter. 



CONDUCTIVITY MEASURING APPARATUS. 



The conductivity was measured with an apparatus of the roller type 

 described by Kohlrausch and Holborn and furnished by Hartmann and 

 Braun. The slide-wire was calibrated by the method of 

 Strouhal and Barus. The resistance coils were of man- 

 ganine and were calibrated by comparison with standard 

 resistances, certified by the Deutsche physikalisch-tech- 

 nische Reichsanstalt. A small induction coil of the ordi- 

 nary form was used, a commutating switch being intro- 

 duced between it and the bridge. It was shown that the 

 mean of the two readings obtained by commutating was 

 the same when the telephone also was commutated and 

 when a Nernst string interrupter was used instead of 

 the ordinary induction coil. 



THERMOMETERS. 



Three different styles of thermometers were used. The temperature of 

 the 18 bath was determined with a 60 thermometer, reading directly to 

 tenths, which was calibrated by comparison with a standard Baudin ther- 

 mometer, certified by the Bureau of Standards of the United States. A 

 Beckmann thermometer was used in the 100 bath; and this was calibrated 

 immediately after each measurement by heating it in steam in a Regnault 

 apparatus. Alvergniat 360 thermometers were used in the other baths. 

 They were first calibrated for irregularities of bore and then at the fixed 

 points 0, 100, 218, and 306. The values of the boiling points of 

 naphthalene and benzophenone determined by Jaquerod and Wassmer 

 were used throughout this whole series of investigations. 



HEATERS. 



Conductivity measurements were made at 18 and at about 100, 156, 

 218, 281, and 306. The first of these temperatures was secured by im- 

 mersing the bomb in a bath of liquid xylene contained in a well-jacketed 

 copper cylinder. The bath could be heated electrically by passing a cur- 

 rent through a platinum helix, or cooled by flowing cold water through a 

 coil of lead pipe. The bath was continually stirred by a propeller, and its 

 temperature was maintained constant to within 0.01. 



The 100 heater was a double-walled copper cylinder heated by steam. 

 The inner cylinder was filled with liquid xylene and the bottom of the 



