DETERMINATIONS OF HEAT CONDUCTIVITY OF SELENIUM. 



361 



The relation between the temperature of measurement 

 and the conductivity was found to be approximately linear. 

 If we express the conductivity (K) at any temperature t by 

 the equation 



K t = K 25 [ 1 + (t - 25) a ] 

 where K25 is the conductivity of that specimen at 25° C, 

 the values of a range from 0*006 to 0*009 for the vitreous 

 discs examined. For crystalline selenium a varied from 

 0*003 to 0*010, the upper limit being generally approached 

 in the case of older discs. 



In Table II are shown the summarized results for the 

 crystalline disc C, illustrating the decrease in conductivity 

 with the age of the specimen. 



The values of the conductivity at 25° O. of all the vitreous 

 discs prepared are collected in Table III. In the first three 

 cases no special precautions were taken to remove impuri- 

 ties, but the fourth and fifth discs were prepared from 

 highly purified selenium. 1 



Table III. — Thermal Conductivity of Vitreous Selenium. 



Disc. 



Age of Disc. 



K25 



1 



7 years 



0-000328 



2 



2 (retested) 



3 



3 (retested) 



4 

 5 



5 days 



1 year 



10 days 



1 year 

 10 days 



2 days 



0-000325 

 0000329 

 0-000293 

 0-000300 

 0-000327 

 0-000312 



These results suggest that the conductivity of vitreous 

 selenium is independent of the age of the disc, and is not 

 greatly affected by the presence of impurities. The varia- 

 tions which occur are possibly due to the existence of small 

 traces of crystalline selenium in the vitreous discs. 



1 Prepared by R. Threfall, Proc. Roy. Soc. A. Vol. 97, p. 167, 1907. 



