They

are mostly reddish or dark colored, and are more difficultly acted on by nitric acid than the corresponding sulphides. Some occur in nature, as rare minerals. [.] Selenide of copper Berzelianite ; Selenide of lead and copper= Zorgite ; Selenide of copper and silver Eucairite ; Selenide of lead Clausthalite ; Selenide of mercury = Tiemannite ; Selenide of mer- cury and lead Lehrbachite ; Selenide of silver= Naumannite ; Selenide of thallium= Crookesite . IMG:content-1173.png:[blocks in formation]