A REVISION OF THE ATOMIC WEIGHTS OF IODINE AND SILVER. 



129 



SPECIFIC GRAVITY OF IODINE PENTOXIDE. 



In order to find out exactly the buoyant effect of air upon the weight of the 

 pentoxide an accurate knowledge of the specific gravity of the substance was 

 necessary. The density was determined by displacement of kerosene of known 

 specific gravity, by pentoxide which had been prepared as previously described 

 by heating in a small platinum boat. The boat was weighed in a small weighing- 

 bottle, and immediately after the weighing the boat was covered with kerosene 

 in the bottle. The bottle was placed in a small vacuum desiccator and the 

 desiccator was kept exhausted with continual jarring until apparently every 

 trace of air had been displaced from the powder. A special pycnometer stopper ^ 

 was next inserted in the bottle and the pycnometer was set while immersed in a 

 water bath at 25° C. 



The Specific Gravity of Iodine Pentoxide. 

 Specific Gravity of Kerosene = 0.7655. 



The vacuvun correction for one apparent gram of iodine pentoxide calcu- 

 lated from the above value for the density is +0.000106 gm., the weights being 

 assumed to have the density 8.3.' A vacuum correction of —0.000031 was 

 applied for every gram of silver. 



A nearly new No. 10 Troemner balance was used in all the weighing. It was 

 readily sensitive to 0.2 mg. The weights were carefully standardized to hun- 

 dredths of a milligram, by the method described by Richards.* 



' For details of pycnometer and setting see Ba.xter and Hines, Amer. Chem. Jour., 31, 220 

 (1904). 



' At 0° Ditte obtained the value 4.487. At 9° Kammerer obtained the value 4.799. Filhol 

 found the density to be 4.250. Dammer. Handb. der anorg. Chem., i, 560. 



^ See page 40. 



* Jour. Amer. Chem. Sac, 22, 144 (1900). 



