SOME STRUCTURAL FEATURES OF SELENIUM DEPOS- 

 ITED BY CONDENSATION FROM THE VAPOR 

 STATE IN THE NEIGHBORHOOD OF 

 THE MELTING POINT^ 



L. E. DODD 



The primary object of this paper is to record some experimental 

 observations. During work- on the vapor tension of the element 

 selenium, above and below the melting- point, where the Knudsen 

 method of molecular flow was used, the condensed material depos- 

 ited itself on the cooling tube of the apparatus in a noteworthy 

 manner. Some numerical data on it in addition to that necessary 

 for the vapor pressure measurements were obtained incidentally at 

 ihe time of the experiments. A description of the behavior of the 

 deposit, from run to run of the pressure measurements, is here 

 given, partly by means of the accompanying tables, including the 

 numerical data mentioned. The type of tube upon which the ma- 

 terial condensed is described in the paper already referred to, on the 

 sublimation curve. Dimensions of tubes E and F, used in two 

 series respectively of pressure measurements, are stated in con- 

 nection with figure 124. 



Table I has reference to a series of eleven measurements on the 

 hexagonal crystalline form of selenium as first produced by Major 

 F. C. Brown,^ and by him furnished to the writer, for the vapor 

 tension work. 



Table II presents the same kind of data for a similar series of 

 thirty measurements on the vapor pressure above the melting point. 

 The material evaporated in this second series was amorphous se- 

 lenium obtained in stick form from Eimer and Amend. 



There are at least two points of interest regarding the deposit, 

 first, deposition in zones of the selenium as it condenses, and sec- 



^The original title of this report as read by proxy before the Academy at 

 its spring- meeting, 1918, did not refer to the selenium deposits condensed 

 from vapor on both sides of the melting point, but only above it. At the 

 present writing (Sept., 1919), however, the data for a series of experiments 

 below the melting point, as well as above it, are at hand, and the scope of 

 the paper has been extended by insertion of Table I, while the discu.ssion of 

 an unusually heavy deposit, mentioned at that time, obtained by a special 

 evaporation not belonging to either of the E and F series of pressure 

 measurements, has been omitted. 



=See paper on sublimation curve for the hexagonal crystals of selenium, 

 this number of the Proceedings. 



^With regard to the method of production of selenium crystals of large 

 size see Brown's paper in Physical Review, 5, pp. 236-237, March, 1915. 



