How is the hydrometer used in measuring the charge of a car battery?
Hydrometer is a long glass capillary with a bulb at the bottom sealed at both ends. The bulb is filled with metallic balls such that the hydrometer when immersed in a column of liquid floats and the liquid level on its stem shows the specific gravity of the liquid. They are available in the range from 1.100 to 1.200, 1.200 to 1.300 and so on. The one having the range 1.200 to 1.300 is used to measure the specific gravity of the sulphuric acid electrolyte in the car battery. In a fully charged car battery, specific gravity of the electrolyte is 1.285. The electrolytic solution is taken in a tall cylinder and hydrometer is immersed in it. It floats in the liquid and the liquid level on the stem of the hydrometer gives the reading of the specific gravity of the liquid.
