The hardness of crushable materials is determined by an apparatus capable of applying a uniformly increasing compression force to the material undergoing test. This force is applied by a plunger exerting a downward pressure on the crushable material and by the weight of a receiving container suspended from the plunger. During the test, the weight exerted by the suspended container is continuously and uniformly increased by the flow of fluid from a reservoir tank into the receiving container. The flow of fluid is commenced by the opening of a normally closed solenoid valve in response to the closing of a relay switch. This switch is adapted to assume an open position when the weight of fluid in the receiving container becomes sufficient to cause the plunger to drop to a lower position upon crushing of the crushable material being tested. The opening of the relay switch, in turn, causes the solenoid valve to close upon crushing of the material being tested. The weight of the plunger and the suspended receiving container, together with the fluid in the container, provides a precise measure of the hardness of the crushable material.