Humboldt State University ® Department of Chemistry
Robert A. Paselk Scientific Instrument Museum
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 1946.2 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 counter. 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 Mettler H10 balances include a taring system, allowing the balance to be zeroed with a weighing container in place, and a filling guide (100 mg range) showing approximate weight while adding material. Detailed descriptions and directions for use are found in the instruction manual.
The Mettler H10 is essentially a replacement for the Mettler H5 with a couple of new features as well as a new style of case. The most noticeable difference for the user is the replacement of the dial with a counter to read the last two decimals (mg and 0.1 mg), giving a somewhat more convenient readout. No catalog description is available in our museum catalogs. However, descriptions are available for the H10T, which has identical specifications, from the 1968 Van Waters and Rogers catalog, Catalog 69 Scientific Apparatus instruments and supplies for: Industrial, Educational, Clinical and Research Laboratories.
This balance was purchased by the chemistry department in 1971 along with five other Mettler H10 balances and one Mettler H10Tw balance. On the 1988 inventory, one of the H10's was in the student research lab (SA 460), the remainder, along with the H10Tw, were all in the analytical chemistry lab balance room (SA 369A).
The single-pan mechanical substitution balance is rapidly being replaced by the electronic balance, introduced in the 1980's, which is even more convenient, as well as more precise and accurate.2
The balance case, of formed aluminum sheets with glass doors, is 16 1/2" high, 9 1/2" wide and 20" deep. The balance has a capacity 160 g., a range of 1,000 mg on the optical scale, an accuracy of ±0.1 mg, and weights adjusted to within Class S tolerances. For more information see the scanned table of H10 specifications. Two views of the mechanism are available. The first image is of the weighing mechanisms with the top of the balance removed and viewed form the right. In the second image the top and left side are removed to expose the weighing mechanisms and the column of the release mechanism. The functionality of the components visible in these images may be clarified by comparison with the scan of the remaining 24" x 36" poster featuring the Mettler H10. Note that the beam and weight hangers are locked for shipping in this balance, as can be seen in the images. An instruction manual for the Mettler H10 accompanies the balance. The chemistry department also had a poster showing the features of the Mettler H10 balance, shown in the scan above..
This balance was taken out of service 9/2/1987 with the note from R. Paselk: "Release mechanism not functioning correctly." It is not currrently functional but, based on inspection, is believed to need only minor adjustments and lubrication.
1 According to the HSU Inventory this balance was purchased in 1971.
2 Kupper, Walter E. "Balance" in McGraw-Hill Eincyclopedia of Science and Technology, 8th ed. v2, McGraw-Hill, New York (1997) p 486.