Humboldt State University ® Department of Chemistry

Robert A. Paselk Scientific Instrument Museum

Standard Cell, Weston model 4

Weston Inst. Div. of Daystrom Inc.

Humboldt College; 1960

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) | CdSO_4(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:

• Duff. Standard Cells for E.M.F. Determinations from A Text-Book of Physics (1921)

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

HSTC (1921-34)

HSC (1954-1973)

HSC (1935-1953)

HSC 1956-72 Instrument Collection

© R. Paselk

Last modified 13 August 2010