DETERMINATIONS OF HEAT CONDUCTIVITY OF SELENIUM. 



363 



affected by factors which influence the electrical conduc- 

 tivity, in the manner stated at the beginning of this paper. 

 Table V. — Thermal Conductivity of Crystalline Selenium. 

 Disc D, prepared at 192° C. on 14 June, 1916. 

 Thickness of disc = 0-6749 cm. 



Date. 



Temperature 

 of disc. 



Thermal 

 Conductivity. 



6 July, 1916 



7 July, 1916 

 10 July, 1916 



12 July, 1916 



13 July, 1916 

 18 July, 1916 



26 ! 64 C. 

 34-22 

 . 41-26 

 27-11 

 51-99 

 25-77 



0-00162 

 000169 

 0-00168 

 0-00165 

 000175 

 0-00173 



While the discs were in position for the thermal deter- 

 minations, a few measurements of the electrical conduc- 

 tivity were made, typical figures being shown in Table II. 

 The results may be summarised thus : — 



(i) The temperature coefficient of the electrical conduc- 

 tivity is positive, 

 (ii) The conductivity of crystalline selenium is much 

 greater than that of the vitreous form; it increases 

 with the temperature of preparation, but decreases 

 with the age of the disc. 

 (iii) In many cases irregularities in the value of the 

 thermal conductivity are accompanied by correspond- 

 ing, but more marked, variations in electrical con- 

 ductivity. 



These results indicate a close, though probably complex, 

 relationship between the thermal and electrical conduc- 

 tivities, and are such as might be expected if the variations 



in the latter were due to changes in the number of free 

 electrons present in the substance. 



In conclusion, I wish to express my indebtedness to Pro- 

 fessor O. U. Vonwiller, under whose direction this work 

 was done, and to Mr. J. J. Forster b.Sc, for his assistance 

 in taking the early measurements. 



