SELENIUM. 



inents in general are made with so much preci- 

 sion that they furnish very good approximations. 



Selenium forms with oxygen an acid, which 

 has been distinguished by the name of selenic 

 acid, and with hydrogen a gaseous compound, 

 which has been called selenietted hydrogen gas. 



1. Selenic acid combines with most bases in 

 two proportions, and with a considerable number 

 in three proportions, forming with them, salts 

 distinguished by the names of seleniates, biselen- 

 iates, and quadroseleniates. Two seleniates have 

 been analyzed by Berzelius : namely, seleniate of 

 soda, and selenlate of barytes. Let us deduce 

 from each of these analyses, the atomic weight 

 of selenic acid. 



(1.) Seleniate of soda does not crystallize Analysis of 



^ ' f seleniate of 



readily, though it may be made to deposite crys- soda; 

 talline grains. The biseleniate crystallizes more 

 easily, and assumes the form of needles. Ber- 

 zelius rendered a given weight of each of these 

 salts anhydrous, mixed each with twice its 

 weight of sal-ammoniac, and applied a subliming 

 heat ; the selenic acid was sublimed and decom- 

 posed, and nothing remained but the base of 

 each salt united to muriatic acid, or rather, in 

 the state of chloride of sodium. 100 parts of 

 seleniate of soda furnished 66 parts of common 

 salt, equivalent to 35 55 soda. Hence, this salt 

 is composed of 



