Improved Mercury Vacuum Pycnometer for Apparent Density Measurements of Granular Materials

Abstract

NOWLEDGE of thc apparent density of solid materials is often useful for determining the porosity of many products and K raw materials. In the usual applied methods' the porous core sample is immersed in mercury with the assumption that mercury, because of its high surface tension, does not penetrate the capillaries. These methods give good results when the sample is large enough to be pushed into the mercury with prongs. This method, however, cannot be used in the case of granular or powdered samples. The use of standard pycnometer bottles causes serious errors because (1 ) many materials have densities less than that of the mercury and will float on its surface, (2) air bubbles are formed between the particles and the pycnometer plug, and (3) a thin layer of air on the surface of the solids may prevent direct contact between the mercury and the solid surface. The pycnometer presented here (Fig. 1) is designed on the same principle as that previously designed by the writer2 but with several improvements. I t avoids the sources of error mentioned and is simple to operate. The weighed sample is placed in the pycnometer and evacuated. The shape of the pycnometer permits the mercury, introduced after evacuation, to squeeze the particles to the convex side of the pycnometer and contact of particles with the pycnometer plug is avoided. The sloping bottom keeps the particles in the lowest part of the pycnometer before the mercury is introduced. As mercury usually contains a small quantity of included air, it is also evacuated before intro-