THE HYDROMETER AND BEAUME GRAVITY An hydrometer is an instrument for determining the density of liquids. It usually consists of three parts: (a) A graduated stem or tube of uniform diameter; (b) a bulb containing air and also a thermometer; (c) a small bulb at the bottom con taining shot which causes the instrument to float in the liquid in an upright position.
The scale may be graduated to read the specific gravity, but when used to determine the density of oils, it usually reads in Beaume degrees.
The graduations on the Beaume hydrometer are the figures of an arbitrary scale, the instrument being made in two forms, one for the density of liquids heavier than water and one for those lighter than water. With the former type, the zero reading corresponds to the specific gravity of pure water, which is Loo, but the scale on the Beaume hydrometer for liquids lighter than water is so graduated that the reading io corresponds to the specific gravity of pure water.
The standard of measurement for the density of oils is the reading of the Beaume hydrometer for liquids lighter than water when the temperature of the oil is F. A rough rule for the correction at
any other temperature is: For every F. above F. subtract one degree from the Beaume reading, and for every 1o° F. below 60° add one degree, thus: The hydrometer indicates a gravity of a certain oil fuel to be "27.5° B." and the temperature of the the oil for this reading is F. The temperature then is 15° F. above F., and the correct gravity is 27.5 - = 26° B.
Or:— The hydrometer indicates a gravity of 24° B. at a temperature of F. Then the correct gravity will be 6o-4o 24 = B.
io Formula for reducing Beaume reading (liquids lighter than water) to specific gravity: Specific Gravity = 140 13o + degrees Beaume Thus: Gravity Beaume = 26 at F.
Specific Gravity = + r .897 (See table, page 131).
4o 20