The Fahrenheit hydrometer is a device used to measure the

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

of a liquid. It was invented by

Daniel Gabriel Fahrenheit Daniel Gabriel Fahrenheit FRS (; ; 24 May 1686 – 16 September 1736) was a physicist, inventor, and scientific instrument maker, born in Poland to a family of German extraction. Fahrenheit invented thermometers accurate and consistent enough t ...

(1686–1736), better known for his work in

thermometry Temperature measurement (also known as thermometry) describes the process of measuring a current temperature for immediate or later evaluation. Datasets consisting of repeated standardized measurements can be used to assess temperature trends. ...

. The Nicholson hydrometer, after William Nicholson (1753-1815), is similar in design, but instead of a weighted bulb at the bottom there is a small container ("basket") into which a sample can be placed.

Operation

The Fahrenheit hydrometer is a constant-volume device that will float in water. In the figure shown here, the hydrometer is floating vertically in a cylinder containing a liquid. At the bottom of the hydrometer is a weighted bulb and at the top is a pan for small weights. To use the hydrometer, one first accurately determines its weight (W) while it is dry. Next, the device is placed in water, and a weight (w) sufficient to sink a marked point on the rod to the water-line is placed on the pan. At that point, the weight of water displaced by the instrument equals W + w. The hydrometer is then removed, wiped dry, and placed in the liquid whose density is to be determined. A weight (x) sufficient to sink the hydrometer to the same marked point is placed in the pan. The density (D) of the second liquid is then given by D = (W + x) / (W + w).See page 170 of
School Physics
' by Elroy McKendree Avery, 1895, American Book Company, New York, from which much of this article is taken. The Fahrenheit hydrometer can be made of either glass or metal.

References

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Operation

References

See also