It often happens in mineralogical inquiries that from scarcity of materials, lack of time, or other causes, the important datum of specific gravity is not secured. Now, however, that Sonstadt has shown us how to prepare a nearly colourless and perfectly transparent liquid with a density three times as great as that of water, there will generally be no difficulty in ascertaining the specific gravity of very many rare minerals as to which our knowledge remains imperfect. More than this, two minerals if of different specific gravities (provided one is less than S.G. 3.0), may often be easily separated from one another if they are in fragments of appreciable size. Thus, pieces of quartz with a S.G. of 2.655 float, while fragments of beryl (S.G. 2.691) sink in a solution having S.G.=2.67. A very simple apparatus is required for the purpose. (See fig. 7, Plate. VIII.)