# Baumé scale

The Baumé scale is a pair of hydrometer scales developed by French pharmacist Antoine Baumé in 1768 to measure density of various liquids. The unit of the Baumé scale has been notated variously as degrees Baumé, , Bé° and simply Baumé (the accent is not always present). One scale measures the density of liquids heavier than water and the other, liquids lighter than water. The Baumé of distilled water is 0. The API gravity scale is based on errors in early implementations of the Baumé scale.

## Conversions

The relationship between specific gravity (s.g.) (relative density) and degrees Baumé is function of the temperature. Different versions of the scale may use different reference temperatures. Different conversions formulae can therefore be found in various handbooks.

As an example, a recent handbook states the conversions between specific gravity and degrees Baumé at a temperature of 60 °F (16 °C):

• For liquids more dense than water, given the degrees Baumé, the specific gravity is: ${\text{s.g.}}={\frac {145}{145-\mathrm {degrees\ Baum{\acute {e}}} }}$
• For liquids more dense than water, given the specific gravity, the degrees Baumé is: $\mathrm {degrees\ Baum{\acute {e}}} =145(1-{\frac {1}{\text{s.g.}}})$
• For liquids less dense than water: ${\text{s.g.}}={\frac {140}{130+\mathrm {degrees\ Baum{\acute {e}}} }}$

An older handbook gives the following formulae (no reference temperature being mentioned):

• For liquids more dense than water:${\text{s.g.}}={\frac {144}{144-\mathrm {degrees\ Baum{\acute {e}}} }}$

• For liquids less dense than water:${\text{s.g.}}={\frac {144}{134+\mathrm {degrees\ Baum{\acute {e}}} }}$

## Definitions

Baumé degrees (heavy) originally represented the percent by mass of sodium chloride in water at 60 °F (16 °C). Baumé degrees (light) was calibrated with 0°Bé (light) being the density of 10% NaCl in water by mass and 10°Bé (light) set to the density of water.

## Other scales

Because of vague instructions or errors in translation a large margin of error was introduced when the scale was adopted. The API gravity scale is a result of adapting to the subsequent errors from the Baumé scale. The Baumé scale is related to the Balling, Brix, Plato and 'specific gravity times 1000' scales.

## Use

Before standardisation on specific gravity around the time of World War II the Baumé scale was generally used in industrial chemistry and pharmacology for the measurement of density of liquids. Today the Baumé scale is still used in various industries such as brewing, sugar beet processing, ophthalmics, starch industry, winemaking and printed circuit board (PCB) fabrication. It is also used for caustic in refining process.