96 



RESEARCHES UPON ATOMIC WEIGHTS. 



silver iodide and asbestos was used in computing the results, the weight of elec- 

 trolyzed silver serving merely as a check upon the weight of silver iodide. 



In order to drive off the last traces of moisture from the silver iodide it was 

 fused in a porcelain crucible. The bulk of the precipitate, freed as completely 

 as possible from asbestos, was transferred to a clean crucible, which was then 

 weighed with its cover. The crucible and cover were placed inside a large porce- 

 lain crucible, and were heated until fusion took place. A temperature much 

 above the melting point of silver iodide was avoided, since this substance is 

 distinctly volatile at higher temperatures. The loss in weight was then deter- 

 mined. The fused salt when cold was light yellow in color, with no trace of 

 darkening, showing that no appreciable loss of iodine had taken place. 



SPECIFIC GRAVITY OF SILVER IODIDE. 



The specific gravity of pure silver iodide was found by displacement of water. 

 Three determinations were made with material which had been fused in a por- 

 celain crucible and cooled by pouring the fused mass upon a cold tile. The 

 solidified salt was broken into small fragments and was introduced into a 

 weighed pycnometer for solids, which was then reweighed. Water sufficient to 

 cover the salt was introduced into the pycnometer and the system was placed 

 in a vacuum desiccator which was kept exhausted until it seemed probable that 

 all air had been extracted from the solid. Then the pycnometer was immersed 

 in a bath at 25° C. and exactly filled with water. Finally the system was 

 weighed. Two more determinations were carried out with material which had 

 been cast into sticks by pouring the fused salt into a porcelain boat. These 



1 The values for the density of silver iodide found by other experimenters are as follows: 



Boullay, yl«M. (/e CAm. e/ (/e PAy^., (2) 43, 266 (1830) 5.614 



Karsten, /oz<r./«> CAew. «n<i PAy^., 65, 417 (1832) 5.026 



Filhol, /lw«. (^g CAiOT. e/ rfePAy^., (3) 21, 417 (1847) S-500 



Schiff, Ann. der Ckem. utid Phartn., 108, 21 (1858) 5.35 



H. St. Clair Deville, Cow/>/cs PewrfziS, 64, 325 (1867) 5.687 at 0° 



Schroeder, Atm. der Chem. und Pharm., 192, 295 (1878) S-650 to 5.718 



