Glass cylinders and spheres were crushed by slow compression in a hydraulic press. In all experiments the elastic energy stored in the specimen prior to fracture was measured. In some experiments the surface area of the resultant powder was measured by gas adsorption; in others the heat generation upon fracture was measured. The latter experiments show that considerable additional energy is fed into the fracturing specimen from the press. Local stress concentrations, and hence energy level at fracture, varied widely with particle shape. Calorimetric experiments suggest that real differences in crushing effectiveness, that is new surface per unit actual work done on the specimen, do occur. These differences are not due directly to the magnitude of the energy fed in from the press but rather to the effectiveness with which the stored or feed-in energy is used.