Usage/History: This balance is designed for the rapid
and simple determination of the specific gravity of solids. According
to the 1941 Cenco catalog it was: "Extensively used in commercial
work for the control of the compounding of rubber, sorting of
minerals etc. May be used for other physical determinations,
such as surface tension measurements in educational laboratories."*
The two pans enable the user to first weigh an object in
the upper pan in air, and then transfer it into the lower pan
suspended in water in a beaker. The specific gravity is determined
by dividing the extension of the spring by the object in air
by the difference between the extensions in air and water. Through
the combination of light and heavy springs, objects with masses
of 1-100 gm may be determined. The Jolly balance was invented
by the German physicist Philipp von Jolly (1809-1884).
Some contemporary/early descriptions of the Jolly Balance
and its use are provided below:
Description: The instrument is comprised of a one
meter+ column supported on a cast iron (black crinkle finished)
tripod, with tapering sigmoidal legs. There is a chrome plated
leveling screw on the end of each leg. The column is made from
a nickel plated brass hollow square (1.9 cm) tube, 107 cm tall,
with a 100 cm scale (graduated to 1 mm, and numbered at 10 cm
intervals) etched onto one side. Three cast brass (black krinkle
finished), riders move along the column: 1) a beaker platform,
with screw operated fine position control moving the platform
relative to a clamping collar; 2) a collar constraining the captured
double hook bob; and 3) the spring suspension hook with vernier
scale and screw operated fine position control relative to a
clamping collar. All clamping and adjusting screws are chrome
or nickel plated. The beaker platform shows the remains of a
BKH decal within the recessed area on top. The double hook bob
has a ring inscribed into the body about 2/3 the way along the
body. There is an oval brass tag stamped HUMBOLDT
S-T-C / 2097 attached with brass pins to the right side
of one of the tripod legs.
The spring ("7580 spring heavy") and aluminum and
glass pans ("7568 scale pan Upper") are replacements
(Cenco, c. 1960).
References:
*Central Scientific Company, Cenco Scientific Instruments
laboratory Appatatus and Supplies Catalog J-141. Chicago
(1941) pg. 31.
The Encyclopedia Americana, International Edition,
v.16. Americana Corporation. New York (1974) p.192.
