Baumé

Baumé [ A. Baumé; France 1728–1804] liquor and food processing. Symbol Bé. A scheme, expressed in degrees, that measures the specific gravity of liquids, primarily in saccherimetry. Many such scales have been used. All employ a hydrometer graduated such that, for some constant m (the modulus), if d is the reading in a solution of specific gravity s, then (d − d_w)s = (s − 1)m, where d_w is the reading chosen for pure water, usually zero. What has been labelled the ‘old’ Baumé scale uses m = 144, apparently based on an interpretation of Baumé's original scale as having 66° Bé for strong sulphuric acid at 15°C, with s = 1.8427, hence m = 144.32. A later interpretation, with 15° Bé for a 15% salt solution at 17.5°C, gave m = 146.78; this became the ‘new’ or Gerlach scale. Glazebrook R. T. (ed.) Dictionary of Applied Physics Vol. 3: Meteorology, Metrology and Measuring Apparatus (London: Macmillan, 1923)
The modern standard for liquids denser than water is m = 145 with 15° Bé for 15% salt by mass in water but a temperature of 10° Réaumur (12.5°C, 54.5°F); example values are:

Specific gravity	1	1.01	1.03	1.1	1.5	2.0
° Baumé	0.72	1.44	4.22	13.18	48.3	72.5

A scale with 0° Bé for 10% salt and 10° Bé for pure water and m = −140 is used for liquids less dense than water (hence having readings greater than 10° Bé); example values are:

Specific gravity	1	0.95	0.9	0.8	0.7	0.6
° Baumé	10	17.37	25.56	45.	70.	103.3

The scheme for API gravity (for petroleum) is structured identically with the less dense Baumé but has a slightly different reference temperature, making its readings generally about 1% greater.