# Baumé hydrometer scale

A hydrometer scale used to indicate the density of liquids. Symbol, °Bé, sometimes °B. One hydrometer is used for liquids denser than water and a different one for liquids lighter than water, and to know what a measurement in degrees Baumé means, it is necessary to know which scale was used.

To calibrate a Baumé hydrometer for liquids denser than water, the hydrometer was immersed in distilled water at 15°C, and the level at which it floated was taken as 0 on the scale (the 0 will be at the top of the scale). It was then immersed in a solution (at 15°C) of 15 parts by weight sodium chloride (common salt) to 85 parts distilled water, and this point was marked 15. The rest of the scale was then marked off at intervals equal to one-fifteenth the distance between the 0 and 15 points.

In the Baumé hydrometer for liquids less dense than water, the 0 point is at the bottom of the scale and is the level at which the hydrometer floated when it was immersed in a solution of 10 parts common salt to 90 parts water by weight, at 15°C. The other fixed point is at 10, and is at the level at which the hydrometer floated in distilled water at 15°C. The rest of the scale is marked off at intervals equal to one-tenth the distance between the marks for 0 and 10.

Unfortunately, early versions of the scale didn't take into account such factors as temperature, and they also didn't have very accurate values for the density of the salt solutions, with the result that 19ᵗʰ century tables (including Baumé's) for converting Baumé degrees to density are not to be trusted.¹ An investigation under the auspices of the U.S. National Academy of Sciences found “twenty-three different scales, published by as many writers, for liquids heavier than water--no one of which can be said to be correct, or to have been obtained by following Baumé's directions.”²

In the United States, the Baumé hydrometer for liquids heavier than water was calibrated by letting 0°Bé be the level in distilled water at 60°F, and 66°Bé the level to which the hydrometer sunk in concentrated sulphuric acid with a specific gravity of 1.8354 at 60°F.

The U.S. Bureau of Standards adopted the following definitions for the Baumé scales.³

For liquids less dense than water,

For liquids denser than water (this definition was adopted for the manufacture of acids and alkalis by the Manufacturing Chemists’ Assn. in 1903),

where “G” stands for the specific gravity of the liquid at 60°F in relation to water at 60°F.

1. E.g., Balfour Stewart and W. W. Haldane Gee.
Lessons in Elementary Practical Physics. Vol. 1.
London and New York: Macmillan and Co., 1904.

Page 149. First edition 1885.

2. C[harles] F[rederick] Chandler.
The Baumé Hydrometers.
Memoirs of the National Academy of Sciences, Volume 3, Part 1.
Washington, D.C.: U. S. Government Printing Office, 1881.

3. U.S. National Bureau of Standards.
United States standard Baumé hydrometer scales.
Bureau of Standards Circular No. 59.
Washington, D.C.: U. S. Government Printing Office, April 15, 1916.

## sources

The [hydrometer] scale most commonly employed in this country in the arts and in commerce are those devised in the last century by Baumé, a Parisian pharmaceutist, and known as Baumé's Hydrometers—one for liquids heavier than water—the other for liquids lighter than water. The latter only will be considered here. The graduation is made as follows: The instrument, with blank scale, is allowed to float in distilled water at 60°F. The point to which it sinks is marked 10°. It is now transferred to water holding in solution exactly ten per cent. of its weight of salt, and the point to which it now sinks is marked 0, the bulb having been previously so loaded with mercury or lead that the point shall fall at the bottom of the scale. The interval between these two points is divided into ten equal parts, and the remainder of the scale is graduated, as far as necessary, according to this basis.

For the purpose of finding the specific gravity corresponding to any degree of the Baumé scale thus constructed, or the reverse, it is customary to use an empirical formula. Different authorities employ slightly different formulae, and hence slight discrepancies occur in the results obtained, as may be seen by comparing the tables given in different works on technology. Amid these discrepancies, and in the absence of any legal authority fixing the value of the degrees of the Baumé scale, it became necessary to select some one formula as the basis of these tables. The preference has accordingly been given to the scale adopted in the latest edition—the thirteenth—of Wood and Bache's United States Dispensary, page 1751. As this scale extends only to 70°, the higher numbers required for the lighter petroleum products have been added.

S. A. Lattimore.
Tables for the Exact and Rapid Computation of the Number of Gallons Contained in any Given Weight of Oil, or Other Liquid Lighter than Water, without Measuring or Gauging.
Rochester, NY: Printed at the Vacuum Oil Co.'s Printing Office, 1912.

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