Standard Cell, Eppley

Eppley Laboratory, Inc.

Humboldt State College; 1959






Use/History: Unsaturated Weston cells, such as this example, are the most common voltage standards in normal laboratory use. This specimen represents a style going back to at least 1929. These cells show a small temperature coefficient and so are normally preferred over the saturated Weston cell. However their e.m.f. decreases by about 0.08 mv per year, and thus must be calibrated periodically against a saturated Weston cell at a defined temperature. The Weston cell may be diagramed as: Cd(Hg) | CdSO4(aq), Hg2SO4 | Hg.
Weston invented and patented the saturated cadmium cell in 1893. It had the advantage of being less temperature sensitive than the previous standard, the Clark cell. It also had the advantage of producing a voltage very near to one volt: 1.0183 V. In 1911 the Weston Saturated Cadmium Cell became the International Standard for electromotive force. Weston waved his patent rights shortly afterword so anyone was allowed to manufacture it.*
Early/contemporary descriptions of the features of the standard cell and its use are provided below:
Description: See research below for general description. The square base of the cell is 4 3/16" dia. and the cell is 5 1/4" high. There is a metal tag on the top of the cell which reads: STANDARD CELL / LOW TEMPERATURE COEFFICIENT STANDARD OF E.M.F. / NO. 19866 / INTERNAL RESISTANCE NOT OVERR 500 OHMS / THE EPPLY LABORATORY, INC. / NEWPORT, R.I. / CAT. NO. 100 MADE IN U.S.A. Typed on a white paper tag is: 1.01924v. 10/20/59. Includes Eppley Laboratory, Inc. Certificate (98k), dated October 20, 1959 for this cell: serial number 708908. Humboldt College decal: 30412.
Research: An identical standard cell is described as item on pg 185 of the Braun-Knecht-Heimann-Co. div of Van Waters & Rogers, Inc, Catalog No. 63 (©1961).
* Woodbury, Edward O. A Measure for Greatness: A Short Biography of Edward Weston. McGraw-Hill Book Company, Inc. New York.
Last modified 18 June 1998