Section 8. Standardization of the Apparatus. 2? 



originally present in the cylinder, the final concentration is easily calcu- 

 lated. After weighing the solution in from the pipette, the bomb is closed, 

 and the air pressure reduced to 2 cm. Upon heating, careful watch is kept 

 of the readings with the auxiliary electrode to make sure that too much 

 solution has not been put in. After the conductivity of the upper chamber 

 has been constant long enough to show conclusively that the temperature 

 has become stationary and that the bomb is absolutely tight (even the 

 slightest leak being of course indicated by a constant decrease in the con- 

 ductivity of the upper chamber), the conductivities between the walls of the 

 bomb and both the upper and lower electrodes are measured carefully, and 

 the temperature of the bath is observed. The experiment is then complete. 

 The ratio of these two conductivities is calculated, and the correspond- 

 ing volume is obtained by interpolation from a plot obtained as described 

 in section 8. This volume, corrected for the expansion of the bomb and 

 then divided by the weight of solution in the bomb, gives the specific vol- 

 ume of that solution at the temperature in question, and this quantity 

 divided by the specific volume of the solution at 4 gives the volume of 

 that quantity of the solution that would at 4 occupy one cubic centimeter, 

 this quantity being most convenient in subsequent computations. 



8. STANDARDIZATION OF THE APPARATUS. 

 THERMOMETERS. 



These were calibrated by the method recommended by Crafts,* first 

 for irregularities of bore and then at the fixed points 0, 100, 218, and 

 306. For the last two temperatures the vapors of boiling naphthalene 

 and of benzophenone were used. These substances were obtained from 

 Kahlbaum, and were purified in the manner suggested by Crafts, until 

 their melting-points came within his limits. The form and dimensions of 

 the vapor bath used in establishing the 218 and 306 points were essen- 

 tially those given by him. To reduce the temperatures lying between the 

 fixed points to the gas scale, Crafts' corrections for French glass were 

 also used, our thermometers being of the same make as those used by him. 

 The values adopted for the boiling-points of the naphthalene and benzo- 

 phenone on the hydrogen-gas scale were, however, those recently obtained 

 by Jaquerod and Wassmer (J. chim. phys., 2, 72; 1904). At the begin- 

 ning every temperature measurement was followed by a lag ice-reading ; 

 but this was found to be unnecessary, since the thermometers showed no 

 lag. The ice-reading was, however, taken frequently, to make sure that 

 the zero did not change from another cause evaporation of mercury 



*Am. Chem. J., 5, 307-338 (1883-84). 



