28 Conductivity of Aqueous Solutions. Part II. 



from the bulb below and condensation in the chamber above. This effect 

 was not apparent even after long use at temperatures up to 280 ; but 

 above this the zero would fall perhaps 0.1 from two or three days' use. 

 When in use at 306, instead of taking an ice-reading the thermometer 

 was first placed in the benzophenone heater and then in the calibrating 

 apparatus containing perfectly pure benzophenone. The difference in 

 reading (usually amounting to 0.1 to 0.2) was deducted from the true 

 boiling-point of benzophenone at the observed barometric pressure. 



Two thermometers were calibrated in this way, and in actual use their 

 corrected readings were always found to agree satisfactorily with each 

 other. 



SLIDE-WIRE BRIDGE AND RESISTANCE COILS. 



The slide wire was calibrated by the method of Strouhal and Barus.* 

 The resistance coils were calibrated by comparison with a standard bridge 

 of the Massachusetts Institute of Technology. 



THE CONDUCTANCE-CAPACITY. 



In order to reduce the observed to specific conductances, the conduct- 

 ance-capacity or so-called " cell-constant "f was determined in the usual 

 manner, by measuring in the bomb solutions of known conductance. For 

 this purpose the measurements at 26 of the solutions of both potassium 

 and sodium chlorides, which were afterward studied at higher tempera- 

 tures, were employed, the mean of the most reliable of them being taken. 

 These data are given in section 13. 



THE VOLUME OF THE SOLUTION IN THE BOMB AND THE CORRESPONDING 



CONDUCTANCE-RATIO. 



It was stated above that the volume of the solution at any time in the 

 bomb was determined by measuring the ratio of the conductances between 

 the walls of the bomb and the lower and upper electrodes respectively. 

 This ratio will hereafter be called the conductance-ratio. Its value is, of 

 course, independent of the nature of the solution in the bomb, and is deter- 

 mined fully by its height in the narrow chamber, and therefore by its vol- 

 ume. To find the values corresponding to different volumes, we proceed 

 as follows : The bomb is first dried by rinsing it with alcohol and ether. 



*Wied. Ann., 10, 326 (1880). See also Kohlrausch and Holborn, Leitvermogen 

 der Elektrolyte, 45 (1898). 



fThe term cell-constant is inappropriate, since the value varies with the temper- 

 ature. We shall adopt the expression conductance-capacity, which seems fairly 

 descriptive, since the quantity may be defined as the specific conductance of a solu- 

 tion which, when placed in the vessel, gives rise to an actual conductance unity. 



