Use/History: 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.
Description: 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.
Research: 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.
