Humboldt State University ® Department of Chemistry
Apparently used to demonstrate the effects of total mass and center of mass in the determination of weight using equal-arm balances. The box had been in the back of a shelf in the stockroom for as long as anyone could remember when it was discarded by the HSU Chemistry department stockroom in 1992. When discovered it took a few days of investigation to find out what it was. Finally, Dr. Russell recognized it. According to John Russell (Professor, HSU Chem. Dept., 1956-92) the device was a demonstrator provided to Mettler sales personnel. It was obtained when Arthur Smith (Professor, HSU Chem. Dept., 1948–1969) requested it as part of a purchase of Mettler balances by the Department in 1960/61. As far as he could remember it was never actively used, except possibly by Dr. Smith.
The device consists of a wooden case (the original hinges are missing and have been replaced with tape and new hinges, The latches are present on either side, though rusty) with the various components in custom-fit compartments as seen in this image. The components include: a gold anodized Al upright column which screws into a threaded insert in the front panel of the case, and which has a small right angle shaft at the top. A turned black anodized hub equipped with ball bearings fits over the shaft. Two Al rods screw into the opposite sides of the hub, each is alternately banded in silver and black at about inch intervals. Two pairs of anodized Al spheres (one red and one blue in each pair), about 1.6 & 2.4 inches diameter, thread onto the ends of the shafts. (One of the shafts has a pin where the spheres are attached so that only blue can be used on one side and only red on the other.) A gold anodized Al pointer then screws into the top of the hub, while a black anodized "T" screws in below to provide adjustments for center of mass (one each slip-on (0.9") and threaded (1"), nickel-plated brass balls) and balance (slip-on, spring-held, about 1.1 inch blue anodized Al sphere). A gold anodized, quarter circle scale clamps onto the shaft through a gold anodized extension. A small (about 0.6 inch) blue anodized ball with attached short shaft slips into a hole on the top of the large blue sphere to act as a weight. The maximum overall dimensions of the assembled apparatus are 15" wide by 15" tall, excluding the base. The balance assembled with the larger spheres is seen in the image above. A second image shows the device assembled with the smaller spheres.