130 . RESEARCHES UPON ATOMIC WEIGHTS. 



ADSORPTION OF AIR BY IODINE PENTOXIDE. 



Since the pentoxide is formed by a process of double efflorescence, it must be 

 extremely porous, with consequently an unusually large surface with relation 

 to its weight. Hence it might be supposed that such a substance could adsorb 

 appreciable amounts of gases, possibly even air. This question was investi- 

 gated with iodine pentoxide by determining the difference in weight of the sub- 

 stance in a vacuum and in air. 



Two weighing-bottles were constructed with long, very well ground stoppers 

 which terminated in stopcocks through which the tubes could be exhausted. 

 These tubes were very closely of the same weight and of very nearly the same 

 internal capacity. The tubes were first exhausted and compared in weight by 

 substitution. Next they were filled with dry air and again weighed, the weigh- 

 ings being carried out with the stopcocks open. Both steps were then repeated 

 with essentially the same results. 



Into one of the tubes was introduced about 25 gm. of carefully dried pentoxide 

 and both tubes were completely exhausted. When the tube containing the pen- 

 toxide was warmed to about 1 50° no perceptible quantity of gas was evolved. 

 After the difference in weight of the exhausted tubes had been determined, they 

 were again filled with dry air and weighed, and the process of exhausting the 

 tubes and filHng them with air was repeated. In all the weighings the tubes 

 were treated as described in the case of the phosphorus pentoxide tubes. 



gm. 



I. Difference in weight of exhausted tubes 0.01405 



I. Difference in weight of tubes filled with air 0.01395 



I. Difference in air content of tubes o.oooio 



II. Difference in weight of exhausted tubes 0.01415 



II. Difference in weight of tubes filled with air 0.01397 



II. Difference in air content of tubes 0.00018 



Average difference in air content of tubes 0.00014 



Weight of tube with iodine pentoxide 58.6353 



Weight of tube 32.7966 



Weight of iodine pentoxide 25.8387 



I. Difference in weight of exhausted tubes, one containing iodine pentoxide 25.85120 

 I. Difference in weight of tubes filled with air at 19° C. and 758 mm. . . 25.84473 



Difference 0.00647 



Average difference in air content of empty tubes 0.00014 



Air displaced by I2O6 at 19° and 758 mm 0.00633 



II. Difference in weight of exhausted tubes, one containing iodine pentoxide 25.85091 

 11. Difference in weight of tubes filled with air at 20° C. and 768 mm. . . . 25.84430 



Difference 0.00661 



Average difference in weight of empty tubes 0.00014 



Air displaced by I2O5 at 20° and 768 mm 0.00647 



The same corrected to 19° and 758 mm 0.00641 



Average weight of air displaced by IjOe at 19° and 758 mm 0.00637 



Weight of air displaced by laOs at 19° and 758 mm. calculated from the 

 density 4.799 0.00649 



