The specific gravity of a liquid may be most readily determined by means of a small glass instrument known as the hydrometer. This instrument floats in the liquid to be examined and the specific gravity of the liquid is determined by noting the point on the stem to which the instrument sinks in the liquid. Since a floating body sinks in a liquid to such a point that the weight of the liquid displaced by the body is equal to the weight of the body, the hydrometer, when provided with a suitable scale, indicates directly the specific gravity of the liquid.