Selenium

(se-lene-um.) [From Gr. selène, the moon.] (Chem.) A non-metallic element much resembling sulphur,discovered by Berzelius in 1817. It forms a brittle, gla y ma of a deep brown color, and a semi-metallic lustre. Sp. gr. 7-696. At the boiling-point of water it softens, and melts at a little higher temperature. It boils below a red heat, evolving a deep orange-colored vapor which condenses as a scarlet powder, or in black fused drops according to the temperature of the receiver. Like sulphur, S. forms several allotropic modifications. At. weight 795. Symbol Se. S. unites with oxygen in two proportions, forming a dioxide (SeO2) and a trioxide (SeO3); the latter is only known in combination. These are analogous to the corresponding oxides of sulphur, and are called selenious and selenic acids. They each form a well-defined series of salts. [s. 811]