Humboldt State University
Robert A. Paselk Scientific Instrument Museum
Jolly Specific Gravity Balance
Humboldt S-T-C; c.1926
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 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).
*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.