Section 89. Apparatus and Method. 241 



gas scale, as given by Crafts.* The correction at 260 was determined 

 by comparison with a platinum resistance thermometer which had been 

 standardized in this laboratory by Mr. R. D. Mailey. The values used 

 for the boiling points of naphthalene and benzophenone were those of 

 Jacquerod and Wassmer;f namely, at a pressure of 76 cm. mercury, 

 217.7 for the former substance and 305.44 for the latter. 



METHOD OF PROCEDURE. 



No important change in the method of procedure as described in Part 

 IV was made. The contents of the bomb were always well shaken within 

 the bath by rotating the bomb several times before and between the 

 readings. Constant uniform temperature was thus quickly obtained, and 

 any contamination in the quartz cup distributed through the whole solu- 

 tion. In the measurements up to 156 the bomb was filled from a pipette 

 with such a quantity of solution that the vapor space at 156 was about 

 7 c.cm. In those extended to still higher temperatures such a quantity 

 of solution was always placed in the bomb as sufficed to fill it within 2 or 

 3 c.cm. at the highest temperature of the experiment in question. The 

 solutions were always placed in the bomb the day they were made up 

 from the stock solution. 



Only after the temperature of the bath had remained constant for at 

 least 15 minutes were final bridge-readings taken; then at five minute 

 intervals, double settings (reversing the commutator) were made with 

 each of three different resistances in the box. Before introducing the 

 most dilute solution of any substance, the bomb was first soaked out by 

 heating with conductivity water or the solution itself to 218 or 306. 

 The solutions successively introduced into the bomb were then always of 

 increasing conductance. Washing with alcohol and ether was avoided 

 as far as possible, as their use seemed to be always followed by greater 

 differences than usual between the initial and final 18 conductances. 



90. PREPARATION OF THE SUBSTANCES AND SOLUTIONS. 



The potassium chloride used for determining the conductance-capacity 

 of the bomb was made from J. T. Baker's "Analyzed C. P." salt, said 

 to contain only " traces" of magnesium and of sodium chlorides. This 

 was precipitated from solution with hydrochloric acid and then showed 

 no flame test for sodium. This precipitated salt was washed with hydro- 



*Am. Chem. J., 5, 307-338 (1883-84). A check on these corrections was obtained 

 by comparing the correction at 218 computed from the bore calibration and the 

 steam and benzophenone determinations, with the actually observed correction in 

 the naphthalene bath. The results agreed within 0.1. A further check was 

 obtained some months later by comparison with a certified German thermometer 

 divided in tenths, between 100 and 200, the greatest discrepancy being 0.2. 



tJ. chim. phys., 2, 72 (1904). 



