of the Elements. 



427 



acid. One gaseous atomic volume of the element unites with 

 two gaseous atomic volumes of hydrogen to form two gaseous 

 volumes of the compound, — the condensation consequently 

 amounting to one-third. Sulphur, selenium, and tellurium ex- 

 hibit a marked similarity and gradation of properties. Oxygen 

 manifests a general resemblance to the other three terms, and 

 appears to bear towards them much the same relation that fluo- 

 rine bears to chlorine, bromine and iodine. The atomic weights 

 and vapour-densities occur in sequence: — 



S = 33 

 Se = 79-2 

 T = 1280 



Sum 239-2 



239-2 



= 79-7 



Mean diflference = 48. 



The atomic weight and specific gravity of oxygen, or 16, is 

 exactly half that of sulphur. The specific heat of the atoms of 

 sulphur, selenium and tellurium, is double that of most of the 

 metals*. The atomic volumes of sulphur and selenium, or 101 

 and 103 respectively, are sensibly equal. The number for tel- 

 lurium is 128, the want of relation being possibly due to a want 

 of correspondence in allotropic condition. 



Oxygen and sulphur, possibly also selenium and tellurium, 

 unite with hydrogen in a second, and probably in several other 

 proportions. The series, including some derived members, is as 

 follows : — 



CPS 



Chloride of 

 sulphur, 



Cl^S^ 



Dlchloride of 

 sulphur. 



H2S3? 



H2S5? 



CPO 



Hypochloroua 

 anhydride. 



CPO^ 



Chlorous 

 anhydride. 



CPO'» 



Peroxide of 

 chlorine. 



CPO^ 



Chloric 

 anhydride ? 



The primary hydrides of sulphur, selenium and tellurium, and 

 their derivatives, unite with oxygen in several proportions : — 



Regnauh, Annales de Chimie et de Physique, 3 ser. vol. xlvi. p. 267. 

 2G2 



