Humboldt State University ® Department of Chemistry

Robert A. Paselk Scientific Instrument Museum

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Standard Cell, Weston model 4

Weston Inst. Div. of Daystrom Inc.

Humboldt College; 1960

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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.

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.1

Early/contemporary descriptions of the features of the standard cell and its use are provided below:

Description

The circular base of the cell is 4 3/16" dia. and the cell is 3 7/8" high. There is a metal tag on the top of the cell which reads: WESTON STANDARD CELL / MODEL 4 NO. 19866 / WESTON INSTS., DIV. OF DAYSTROM, INC., / NEWARK, N.J., U.S.A. There is a decal under the cell: Dec. 21 '59. Includes National Bureau of Standards Certificate, (80k) dated March 1, 1960, and Weston Instruments Certificate, (132k) dated February 26, 1960 for this cell: number 19866. (Humboldt College decal: 30642, now removed.)

Research

This standard cell is described as item 79435-37 "Weston Model 4 Cell, Unsaturated" on pg. 703 of the Cenco Catalog J-300 from the Central Scientific Co. (1960) It is also shown as item 19850 on pg 185 of the Braun-Knecht-Heimann-Co. div of Van Waters & Rogers, Inc, Catalog No. 63 (©1961). The same cell, with the same catalog number, is also shown in previous BKH catalogs back to a least as early as 1929 (Catalog No. 29).

1 Woodbury, Edward O. A Measure for Greatness: A Short Biography of Edward Weston. McGraw-Hill Book Company, Inc. New York.

From the Analytical/Physical Chemistry Lab - Exhibit Catalog

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HSTC (1921-34)
HSC 54-73 icon
HSC (1954-1973)
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HSC (1935-1953)

HSC 1956-72 Instrument Collection

© R. Paselk
Last modified 13 August 2010