Hydrometers are commercially available to measure not only Specific Gravity, but concentrations of specific solutions such as salt and alcohol solutions, as well as ☋rix, ☊PI, and other Specific Gravity scales. For accurate results, however, care must be exercised to insure that measurements are made at the correct temperature, i.e., the temperature stated on the Hydrometer at which it was calibrated. Specific Gravity of liquids is most conveniently measured using a Hydrometer. Other common arbitrary scales for Specific Gravity are degrees API (American Petroleum Institute), or degrees Brix, a scale used mainly in the sugar industry, where ☋rix is equal to the sucrose content (weight percent) of sucrose syrups. It is used to express the Specific Gravity of liquids and involves two formulas, one for Specific Gravities less than one, and another for Specific Gravities greater than one.
Among them is the Baumé scale, developed by a French Chemist, Antoine Baumé, around the year 1800. There are also various arbitrary scales used to express Specific Gravity. The Density of a substance may be calculated by multiplying the Specific Gravity by the Density of water at the reference temperature. Since Specific Gravity is a ratio, it has no units, but it is dependent upon both the temperature of the substance and the temperature of the water reference.ĭensity and Specific Gravity are never the same, because Density has units and Specific Gravity is dimensionless, but they are numerically equal when three conditions are met: (1) Density is measured in grams per cubic centimeter, grams per milliliter, or kilograms per liter (2) Density and Specific Gravity are measured at the same temperature and (3) the Specific Gravity is referenced to water at 4☌, where its Density is very close to 1 gram per cubic centimeter. Specific Gravity, on the other hand, is defined as the weight of a sample, at a given temperature, divided by the weight of the same volume of water, at the same temperature or a different specified temperature. It is usually measured in grams per cubic centimeter, grams per milliliter, pounds per cubic foot or pounds per gallon, and is somewhat dependent on temperature and, to a lesser extent, pressure. Density is defined as the ratio of the mass (weight) to volume of a substance. Density and Specific Gravity are related concepts that are often confused.
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