156 PROCEEDINGS OF THE AMERICAN ACADEMY. 



In these two experiments, -when air was admitted, the counterpoise 

 gained 0.00028 and 0.00021 gram respectively (average 0.00025) more 

 than the tube which was later to contain the silver phosphate. After 

 22.69 grams of pure dry silver phosphate had been placed in the tube, 

 the tube and its counterpoise were exhausted and the difference in 

 weight determined. When dry air at 25° C. and 766 mm. was admitted 

 to both the tube containing the silver phosphate and the counterpoise, 

 the counterpoise gained 0.00443 gram more than the tube. Therefore 

 the air displaced by the silver phosphate was 0.00443 — 0.00025 = 

 0.00418 gram. Since 22.69 grams of silver phosphate of density 6.37 

 have a volume of 3.56 c.c, the volume of pure air displaced at 25° C. 

 and 766 mm. should weigh 0.00425 gram. 28 



The experiment was then repeated. After the air had been ex- 

 hausted from the tube and its counterpoise, the tube containing the 

 silver phosphate was heated gently. No gas was evolved. The tube 

 and its counterpoise were then weighed by substitution. When dry 

 air at 24.5° and 767 mm. was admitted to both, the counterpoise 

 gained 0.00445 grams more than the tube containing the silver phos- 

 phate. Therefore the air displaced by the silver phosphate was 

 0.00445 — 0.00025 = 0.00420 grams, whereas the weight of air dis- 

 placed, calculated from the density of the salt, is 0.00426 gram. 



The agreement between the experimental results and those calcu- 

 lated from the density of silver phosphate on the assumption that no 

 adsorption takes place is close enough to show that no significant 

 amount of adsorption occurs. 



Discussion of the Results. 

 i 

 The following table contains all of the analyses not vitiated by a 

 known impurity in the sample or by an accident during the analysis. 

 One feature of this table requires further explanation. In Analysis 5 

 the silver was determined by precipitation as chloride instead of 

 bromide. For every gram of silver phosphate there was obtained 

 1.02707 grams of silver chloride. Since Baxter found AgBr : Ag Cl = 

 1.31017 : 1.00000, 29 this analysis indicates that one gram of sample N 

 is equivalent to 1.02704 X 1. 31017 = 1.34560 grams of silver bromide. 

 This result is placed in the table for comparison with the other analyses 

 and is used in the computation of the mean. 



28 Rayleigh's value for the density of air at 0° and 760 mm., 1.293 grams 

 per liter, is used. Proc. Roy. Soc, 53, 147. 



29 These Proceedings, 1906, 42, 213. 



