Precision Hydrometer Set

Robert A. Paselk Scientific Instrument Museum

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Hydrometers are used to measure the specific gravity of a liquid. Concentration can then be determined for liquids of known composition. For example, the strength of battery acid (a mixture of sulfuric acid and water) in lead batteries is commonly determined with hydrometers. Hydrometers have also been very important historically for determining the "proof" of alcoholic beverages (nearly pure mixtures of alcohol and water).

Hydrometers were described by the Greeks nearly 2,000 years ago. The oldest examples of hydrometers still in existence are of weighted ivory dating to the seventeenth century. Copper hydrometers were developed in the early eighteenth century for determining alcohol proof for taxation. Robert Boyle described a hydrometer in 1675 for the detection of counterfeit coins that differs little from the modern instrument.

The set consists of: 20 precision hydrometer spindles (13" long with 1" dia bulb) covering a range of specific gravity from 0.700 - 1.950 by 0.001 units, two hydrometers with enclosed thermometers for range selection (0.7 - 1.0 and 1.0 - 1.95), and a thermometer (30 - 220°F). The set is housed in a fitted blue velvet-lined black leatherette covered case (19 1/2" w x 19" deep x 2" high). There is a yellow decal on the top of the case: STATE OF CALIFORNIA / HUMBOLDT COLLEGE / 15390.
This set and the individual hydrometers are described as items 16750 (set) and 16752-x (individual) on pg. 260 of the Cenco Catalog J-300 from the Central Scientific Co. (1960). The same hydrometers and set are also described, with the same catalog numbers, in Cenco Catalog J-150 (1950), and Cenco Catalog J-141 (1941).


References:
A. D. Morrison-Low in Bud, Robert and Deborah Jean Warner, eds. Instruments of Science: An Historical Encyclopedia. Garland Publishing, Inc. New York (1998), pp311-13.
Turner, Gerard L'E. Nineteenth Century Scientific Instruments. Sotheby/U Cal., London/Berkeley (1983), pp 89-94.