EEACTIONS OjST PLASTER OF PARIS TABLETS. 79 



Mercury — Grey coating. (Most minerals containing mercury deposit metallic mercury on 

 plaster tablet wlien treated with 0. F.) 



Tellurium — Brownish-black coating, near assay. 



Carbon — Black coating, near assay. (Substances containing easily-decomposed hydro- 

 carbon deposit the black coating of carbon when treated with 0. F.) 



Cadminum — Yellow coating over brownish-black. 



Gold — Purple coating, near assay. 



