An apparatus used to determine the specific gravity or density of soils, or of rock or mineral fragments (see density determination). It consists of a small bottle fitted with a ground glass stopper, with a capillary opening to allow air to escape. The bottle is filled with a reference liquid of known specific gravity, e.g. water or mercury, and weighed, then emptied and filled with the specimen liquid and weighed again. The specific gravity or density is calculated from the difference in weights. It is also possible to determine the specific gravity or density of a powder or gas using a pycnometer.