Humboldt State University ® Department of Chemistry
Robert A. Paselk Scientific Instrument Museum
Analytical Balance, Single-Pan, Substitution-Mettler H5
The single-pan, substitution balance is much faster and more convenient then the traditional two-pan, equal-arm balance. It thus rapidly replaced the older type after its commercial introduction by Erhard Mettler in 1946.1 In this type of balance the pan and weights are counterbalanced by a single fixed weight on the long end of the beam. Weighing is accomplished by removing the built-in weights to compensate (within 1 g) for objects placed on the pan. The final 1 g is read off to 0.1 mg from an illuminated/projected optical scale attached to the long end of the beam and adjusted with a dial. Because the total mass on the balance remains essentially constant in all weighings, weighing precision also remains constant over the range of the instrument. This is in contrast to the double-pan balance, where precision decreases with load. The single-pan mechanical analytical balance is rapidly being replaced by the electronic balance, which is even more convenient, as well as more precise and accurate, introduced in the 1980's.1
The balance case, of molded plastic with an aluminum base-plate, is 15 3/4" high, 8 1/4" wide and 13 3/8" deepThe balance has a capacity 160 g., a range of 1200 mg on the optical scale, an accuracy of ±0.1 mg, and weights adjusted to within Class S tolerances.
The balance on display is set up with a special Mettler clear plastic demonstration top to allow students to see the inner workings. The chemistry department had a single balance set up in this fashion which would be moved to various labs when introducing the use of the Mettler balance. Three views of this balance are provided: Mettler demonstration balance, right-side view; Mettler demonstration balance, left-side view; Mettler demonstration balance, top view.
A folder included with the balance contained the following: Mettler (brochure listing Mettler Analytical, Multi-purpose and Precision balances), Test Test Test (brochure on weighing errors), unpacking/setting-up card, annual service agreement card, Xerox sheets detailing balance tables, and two brochures: Mettler, Multi-Purpose Balances Directions for Use (brochure), Mettler Service (brochure).
The chemistry department also had a number of posters showing the features of the Mettler balance. A scan of the remaining 24" x 36" poster featuring the Mettler H10 is displayed.
An identical balance is shown under "Mettler Multi-Purpose Balances, H5, H4 & H3" Catalog No. 11465, on pg. 25 of: Braun-Knecht-Heiman-Co. (Division of Van Waters & Rogers, Inc.) Catalog No 63, Laboratory Instruments Apparatus and Supplies. San Francisco. (1961). According to the HSU Inventory this balance was purchased in 1962 for $676.00. Humboldt College Tag: 32644
1 Kupper, Walter E. "Balance" in McGraw-Hill Eincyclopedia of Science and Technology, 8th ed. v2, McGraw-Hill, New York (1997) p 486.