Hydrometers are used to determine the specific gravity of a liquid. Consists of a long glass tube containing a ballast at the base of the float bulb and graduations on the stem. The ballast is made from steel pellets free from lead and mercury.
The Baume scale originally was used in industrial chemistry and pharmacology, but today it is used in brewing, winemaking, sugar beet processing, ophthalmics, and the starch industry. Although specific gravity is a dimensionless number, the Baume scale is graduated in degrees Baume. According to Perry's Chemical Engineers' Handbook (8th Edition), °Be' = 145 – 145/sp gr (heavier than water), and °Be' = 140/sp gr - 130 (lighter than water).