THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



SEPTEMBER 1895. 



XIX. The Electrical Properties of Selenium. 

 By Shelford Bidwell, M.A., F.R.S.* 



§ 1. Preliminary^. 



SELENIUM, which is supposed to be an elementary 

 substance, is capable of existing in several distinct modi- 

 fications. The amorphous variety consists either of a finely 

 divided red powder, or of a vitreous mass which resembles 

 black glass in appearance and does not conduct electricity. 

 Amorphous selenium melts at about 100° C , but at tempera- 

 tures between 100° and 217° the black semi-liquid mass 

 gradually hardens into a grey metallic-looking solid. This 

 consists of Se in the crystalline form : it melts at 217°, and is 

 a moderate conductor of electricity, its conductivity being 

 temporarily increased by the action of light. This peculiar 

 influence of light upon Se has attracted much attention, and 

 below is given a list of published papers relating to the 

 subject J. 



* Communicated by the Physical Society : read June 28, 1895. 



f A summary of the principal results will be found at the end of 

 the paper. 



X Willoughby Smith, Journ. Soc. Tel. Eng. ii. p. 31 ; Earl of Rosse, 

 Phil. Mag. March 1874, p. 161 ; Sale, Proc. Roy. Soc. 1873, p. 283 ; Phil 

 Mag. March 1874 ; Werner Siemens, Phil. Mag. November 1875, p. 416 . 

 Draper and Moss, ' Chemical News,' xxxiii. p. 1 ; Moss, Proc. Roy. Soc 

 May 11, 1876; Adams and Day, Proc. Roy. Soc. 1876, p. 113; Phil 

 Trans. 1877, p. 313 ; C. W. Siemens, Proc. Roy. Inst. 1876, p. 68 ; Sabine, 

 Phil. Mag. June 1878, p. 401 ; Graham Bell, < Nature,' xxii. p. 500 ; 

 Proc. Nat. Acad. Sci. April 1881 ; Shelford Bidwell, Phil. Mag. April 

 1881, January 1883, August 1885, March 1891; Fritts, 'Electrical 

 Review,' March 7, 1885, p. 208; Minchin, Phil. Mag. March 1891, p. 207. 



Phil. Mag. S. 5. Vol. 40. No. 244. Sept. 1895. R 



