STRUCTURAL FEATURES OF SELENIUM 



503 



zone, by a process incidental to the condenssftion. It would seem 

 that these molecules had been crowded out from below. The trans- 

 parent middle zone may possibly be a continuation of the first zone, 

 wihich becomes red, a characteristic selenium color, by transmitted 

 light when opacity ceases. But since a thin layer of red material 



FIGURE 125 



was frequently noted beneath the material of zone 1 and next the 

 glass, there is some reason for doubting this. Conceivably both this 

 red substratum and zone 2 are made up of substance deposited in 

 the brief interval required for the vacuum to reach the required 

 stage. 



Egerton,* in describing similar work on the vapor tension of zinc 

 and cadmium, using the same method of molecular flow, speaks of 

 zones of different thicknesses on the condensation tube. But he 

 makes no mention of differences in color, and suggests that mole- 



<Phn. Mag-., V. 33, 193, p. 33, Jan., 1917. 



