Various labs require the measurement of the specific gravity of liquids. This is where laboratory Hydrometer step in. The specific gravity of a liquid is the relative density that is equal to the ratio of the density of the liquid to the density of water. A laboratory hydrometer is generally a long cylindrical stem that consists of a bulb weighted at the bottom. The bulb either has mercury or lead that floats upright and lends stability in water. A scale is also printed on the side that allows the user to know about the specific gravity of the liquid. You are free to choose a glass hydrometer based on the industry where you are working. As its use varies depending upon the type of liquid.