A hydrometer is an elongated glass bulb with a long, thin glass stem rising from the top of the bulb (Figure 1). The bulb is hollow except for a plug of lead in the bottom. If the bulb is inserted into a suspension, it will sink until the force of buoyancy is just sufficient to balance the weight of the hydrometer. The hydrometer is designed to sink into the suspension until the bulb is totally immersed, and the stem protrudes above the surface of the suspension. Because the length of stem that protrudes above the surface is a function of the density of the suspension, more of the stem protrudes for denser suspensions. It is thus possible to calibrate the hydrometer to read various densities. Soil hydrometers are typically calibrated to read in g/ml or g/liter. Hence, an appropriate hydrometer can be inserted into a suspension and a reading taken to obtain the average concentration of the solids in the fluid displaced by the hydrometer. Because the hydrometer calibration is affected by temperature and the specific gravity of solids, these factors will have to be taken into account during the experiment.