A new reference method for testing hydrometers

The two methods for determining the density or specific gravity of liquids used in testing hydrometers are: (1) comparison with standard reference hydrometers, and (2) hydrostatic weighing. In this paper, a new method for the determination of the density of liquids for the testing of hydrometers is described. The method involves determining the differential pressure between two points or planes separated vertically in a liquid and dividing the differential pressure by the product of the local acceleration due to gravity and the vertical separation. The system is based on sound scientific principle, is easy to use, is very precise, and is easily and accurately calibrated using water. The results for such a system are demonstrated for water and for nitric acid solutions. The precision is shown to be approximately 1 part in 10 000 or 0.01%, which is ideal for the testing of hydrometers the precision of which is about 1 part in 1 000 or 0.1%.