188 PROCEEDINGS OF THE AMERICAN ACADEMY. 



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 Eesistance Coils. — The slide wire was calibrated 

 by the method of Strouhal and Barus.* The resistance coils were cali- 

 brated by comparison with a standard bridge of this Institute. 



The Cell-Constant. — In order to reduce the observed to specific con- 

 ductivities, the "cell-constant" was determined in the usual manner, 

 by measuring in the bomb solutions of known conductivity. . For this 

 purpose the measurements at 26° of the solutions of both potassium and 

 sodium chlorides, which were afterward studied at higher temperatures, 

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

 (See Section XI.) 



The Volume of the Solution in the Bomb and the Corresponding Cell- 

 Constant 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 

 conductivities between the walls of the bomb and the lower and upper 

 electrodes respectively. This ratio will hereafter be called the cell- 

 constant ratio. Its value is, of course, independent of the nature of the 

 solution in the bomb, and is determined fully by its height in the nar- 

 row chamber, and therefore by its volume. To find the values corre- 

 sponding to different volumes, we proceeded as follows : The bomb is 

 first dried by rinsing it with alcohol and ether. Some 0.02 molar po- 

 tassium chloride solution f is then boiled to free it from air, and right 

 after cooling, enough of this to fill the bottom part of the bomb to within 

 1-2 mm. of the flange is weighed in from a pipette. The mouth of the 

 pipette is kept under the surface to diminish the absorption of air. The 

 cover is next put on and screwed down, care being taken not to tip 

 the bomb enough to get any of the solution up onto the mouth of the 

 tube Ti. By means of the water pump the air pressure in the bomb is 

 reduced to about 2 cm., and the valve is then closed. If the air is not 

 removed from the solution at the start, it comes out rapidly upon re- 

 ducing the pressure and spatters some of the solution up into the tube 

 Ti, thus allowing it to be swept out by the air current. 



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

 der Elektrolyte, 45 (1898). 



t The reasons for taking tliis solution instead of pure water are that it makes 

 tlie conductivity at tlie upper electrode high enougli to give a good minimum, and 

 that the solution is so strong that contamination could not possibly make any 

 trouble. 



