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504 IOWA ACADEMY OF SCIENCE Vol. XXVI, 1919 



cules of different ranges are present in the vapor. 

 It may be supposed that atoms in different states 

 of aggregation in the molecules account for two 

 or more different molecular types, and that these 

 different types are re-evaporated from the con- 

 densation surface, according to Langmuir's view, 

 before they finally settle permanently in posi- 

 tion, such re-evaporation taking place with dif- 

 ferent degrees of ease for the various types, so 

 __^ that a kind of sifting of the molecules is effected. 



At any rate it would appear that molecular flow 

 as applied in the vapor pressure work men- 

 tioned might be used for a separation of mole- 

 "^ cules of different types, mixed in the vapor state, 



whether these types belong to the same element, 

 FIGURE 126 oi* substance, in different states of atomic aggre- 



gation in the molecules, or whether they are of 

 different elements, or substances.^ If such sepzf- 

 ration in reality occurs for the vapor molecules 

 of different elements, then the method of molecular flow, with 

 condensation at one end of the flow, ought to be available as a 

 method of purification. 



With special reference to the two general characters of series E, 

 the runs not indicated in the tables as of character either "a" or "b," 

 are probably in all cases "a," which was the usual form of the 

 deposit. In fact, it was not until the sixth run that a new character, 

 that subsequently designated "b," appeared. A note made at the 

 time of this run, when the changed appearance of the condensed 

 selenium could not escape notice, reads : "Character of zone 1 has 

 changed somewhat. Instead of rather sharp margin this zone 

 gradually shades off into zone 2, with the addition of an intermediate 

 zone between the region of dull luster of zonie 1 and the trans- 

 parent zone 2, which appears black and glossy. This intermediate 

 zone is translucent over much of its length. Nodules, small but dis- 

 tinct, and with fortuitous distribution, on end of tube, extending- 

 up over bend to sides." A similar note with reference to the eighth 

 run of this series states : "Many nodules on end and sides in zone 

 1. Deposit more like that of E6 than of E7. Zone 3 noted to be 

 opposite deposit on outside tube ; but in E9, while zone 3 is about 



•^In this event an interesting question for experimental study would be, 

 how susceptible to such a separating effect are molecules of mixed vapors 

 of different elements, where the molecules all have the same number of 

 atoms. 



