506 M. Regnault on the Specific Heat of Simple Bodies, 



tity of selenium. I seized on this opportunity to make some 

 new experiments, which have led me to observe many curious 

 properties of this body. This selenium is not quite pure, it con- 

 tains about 2 per cent, of tellurium ; but this quantity is far too 

 small to modify the physical properties of the body, M. Salvetat 

 obtained from an analysis the following results : — 



Tellurium 2*25 



Sulphur traces 



Selenium (from the difference) . 97*75 



10000 



Berzelius thus describes the physical properties of selenium 

 (second edition of the French translation, vol. ii. p. 189) : — 

 " When selenium cools after having been distilled, it assumes a 

 mirror-like surface, of a deep colour, verging towards a reddish- 

 brown, and having a metallic lustre rather like polished haema- 

 tite. The fracture is conchoidal, vitreous, having a leaden-gray 

 colour and a metallic lustre. When allowed to cool slowly after 

 having been melted, its surface becomes unequally granular, of 

 a leaden-gray, and ceases to reflect. It has a fine-grained frac- 

 ture, is rough, and the mass is extremely like a fragment of 

 metallic cobalt. Fusion, followed by a sudden cooling, destroys 

 this appearance, and gives to selenium the characters which I 



described at first When selenium is reduced to powder, it 



becomes of a deep red, but has a strong tendency to collect 

 together at various points : the friction of the pestle imparts to 

 it a polish, and turns it gray, as is the case when bismuth and 

 antimony are powdered. In thin plates selenium is transparent, 

 and has a deep ruby-red colour. It is softened by heat, becomes 

 semifluid at 100 degrees, and fuses completely a few degrees 

 above. In cooling, it remains for some time soft, and may then, 

 like sealing-wax, be drawn into slender and very flexible threads, 

 which, when flattened slightly, care being taken to keep them 

 soft, show better than any other form the transparency of sele- 

 nium. In reflected light these threads are gray, and have a 

 metallic lustre ; viewed by daylight they are transparent, and of 



a ruby-red I found its specific weight to vary between 



4*30 and 4-32. A slow cooling and a grained fracture have no 

 influence on its density." 



According to M. Sacc {Ann. de Chim. et de Phys. 3rd series, 

 vol. xxi. p. 120), selenium softens at 200, and melts completely 

 at 250 degrees. When cooled, it commences to become viscous 

 at 150 degrees ; at 200 degrees it ceases to adhere to the bulb of 

 the thermometer ; at 155 degrees it sticks to the sides of the 

 vessel, and solidifies completely at 1 50 degrees ; from whence 

 we may conclude that its melting-point is 200 degrees, and that 



