502 



IOWA ACADEMY OF SCIENCE Vol. XXVI, 1919 



ond, the existence of two general characters of the deposit in the 

 E series. 



The three zones can be readily distinguished in the photograph, 

 figure 125, although they are actually much more sharply differen- 

 tiated as to appearance than in the photograph. Figure 126 shows 



Fig. 124. See legend below. 



Lengths in cms. Tj=condensation tube 



T,_,=outside tube 

 C =condensation chamber 

 Ev=evaporation chaimber 

 P =platinum partition 



Z.t)* I 4.3 



*Outside measurement. 



how the lengths of the zones are indicated in the tables. The zone 

 nearest the end, or rather at the end and spreading up the sides of 

 the tube for two or three centimeters, which will be referred to as 

 zone 1, contains by far the greater weight of the condensed selenium, 

 and is opaque over the major part of its length, with a dull lustrous 

 appearance by reflected light. Zone 3 lies farthest up the tube, and 

 farthest away from the apertures in the platinum partition where 

 the molecules enter the condensation chamber. This upper zone has 

 a dark, dirty color, and is fairly opaque by transmitted light. There 

 is a possibility that this consists of impurity in the selenum, although 

 this zone was present in some runs of the F series, where crystals 

 supplied the vapor. Whatever the explanation, there must have 

 been a separation from the others of the molecules making up this 



