Humboldt State University ® Department of Chemistry

Robert A. Paselk Scientific Instrument Museum

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Student Analytical Balance

William Ainsworth

Serial No. 32372

Humboldt State College; 19561

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Usage/History

 
The analytical balance is the most fundamental tool in the chemists arsenal. It is used to determine the masses of, or in other words the amount of stuff in, objects or samples. The balance is a comparison instrument. It compares standard or known weights placed on the left-hand pan to unknown samples or objects placed on the right-hand pan. The current instrument also has a rider (a 10 mg bent wire weight which is moved along the graduated scale on the top of the beam) to measure small (1-10 mg) differences in mass. The glass case is to protect the balance from drafts while samples are being weighed, as well to keep the delicate mechanisms free from dirt. This particular model is in Ainsworth’s lower quality line, intended for student work in beginning analytical chemistry, for routine work and as a secondary balance in industrial work. The scanned catalog description is from the Braun-Knecht-Heiman-Co. (Division of Van Waters & Rogers, Inc.) Catalog No 63, Laboratory Instruments Apparatus and Supplies, San Francisco (1961).

This balance, and a second described below, was originally in the Physics department inventory, apparently acquired in 1956. In their 1987 inventory it is listed as Physics property in a Chemistry lab. Apparently the balance was "loaned" to Chemistry prior to 1987. It was used in the old qualitative analysis (Chemistry 1-C) balance room in Science B prior to moving to the "new" chemistry labs on the fifth floor of the west wing of Science A c. 1987. The balance was then moved to the balance room of Science A 571 for use as a demonstration two-pan balance in general chemistry (Chemistry 109).

Early descriptions of the balance and its use are provided below:

Description

Ainsworth type LC analytical balance. This is a rider balance with a capacity of 200 gm on each pan and a sensitivity of 0.1 mg at full load. Weights up to 10 mg are added with the rider. The beam is 6” long of aluminum and is graduated from 10-0-10 mg by 0.1 mg (see close-up of the beam of the balance with serial number 34446, below). The balance case is aluminum, 18”x 18”x 9”, with a hammertone tan finish, and a single counterpoised door.  The base is black slate. The hardware is lacquered brass, including four leveling screws. Additional description is found in the catalog scan. All exterior brass fittings are lightlycorroded.  Interior brass is in very fine, fully functional condition. There is a small black and nickel tag affixed to the front of the balance case: SCIENTIFIC SUPPLIES CO. / SEATTLE, WASH. There is a decal property tag: STATE OF CALIFORNIA / HUMBOLDT COLLEGE / 14979.

A second, later balance (serial number 34446, see close-up of indicator scale) is currently used for demonstration purposes in general chemistry labs. This balance is identical except that the rider moving mechanism is steel (stainless?) rather than laquered brass, as can be seen in the image. There is a decal property tag: STATE OF CALIFORNIA / HUMBOLDT COLLEGE / 15140. When surplused by Physics this balance had been modified to act as an electrostatic balance with one pan replaced by a thin aluminum disk attached to a glass rod and thin wire replacing the sample pan. A non-magnetic stainless steel framework was also present. The balance was returned to its original state when it was transferred to Chemistry for its current use as a demonstration balance.

A small metal Ainsworth rider "pill-box" with rider found with the balance when it resided in the qualitative analysis balance room is also displayed. The rider was sandwiched between paper tissues, one of which is seen next to the box.

1The 1987 HSU Physics Dept. property list shows an acquisition date of 10/56 for property number 14979 and 2/57 for property 15140.

The Chemical Balance at Humboldt

 HSTC icon
HSTC (1921-34)
HSC 54-73 icon
HSC (1954-1973)
HSC 35-53 icon
HSC (1935-1953)

HSC 1956-72 Instrument Collection

© R. Paselk
Last modified 13 August 2010
All photographs © R. Paselk