electrostatic analytical balance
Date: circa 1930
Inventory Number: 2006-1-0104
Classification: Analytical Balance
Subject:
Maker: Empire Laboratory Supply Company, Inc. (ca. 1917 - 1939)
Cultural Region:
Place of Origin:
Dimensions:
51 x 42 x 27.5 cm (20 1/16 x 16 9/16 x 10 13/16 in.)
Accessories: small plastic box of weights; solid aluminum cyclinder marked "3"; large cyclinders (to be connected to power source and meter) (2); plexiglass stand for cylinders; sliding weights (2)
Description:
Standard-looking wood and glass-enclosed two-pan analytical laboratory balance that has been retro-fitted by a user for the electrostatic measurement of mass by the replacement of one of the pans by a system of two metallic cylinders, one fixed to the floor of the case while the other hanging from the balance beam. It rests on leveling screws.
Pillar of balance is marked: "Prae [AS] cision / Germany". A modern notecard from inside the scale is marked: "Balances are very delicate and fragile! So handle most gently. Do not go "poking around" at balance parts." Another one on fiberboard base sheet is marked: "Turn voltage back to zero before snapping power off. Voltage may take ca 2 min. to come on. Measure diameters of cylinders on spare set (Do not take cylinders out from balance." Weight set inside balance is marked: "Physics 13b".
Pillar of balance is marked: "Prae [AS] cision / Germany". A modern notecard from inside the scale is marked: "Balances are very delicate and fragile! So handle most gently. Do not go "poking around" at balance parts." Another one on fiberboard base sheet is marked: "Turn voltage back to zero before snapping power off. Voltage may take ca 2 min. to come on. Measure diameters of cylinders on spare set (Do not take cylinders out from balance." Weight set inside balance is marked: "Physics 13b".
Signedon plaque: Empire Laboratory Supply Co. Inc. / Chemical & Bacteriological / Supplies / New York
FunctionThis balance works by the attraction that two oppositely charged metallic objects, in this case cylinders, exert on each other. If one connects each cylinder to opposite poles of a voltage source, they will after some time acquire a maximum charge with the effect of pulling the hanging cylinder downwards. This downward force depends on the applied voltage, so one can deduce the weight on the balance tray from the voltage one needs to apply to keep the system balanced.
The conversion of this balance to an electrostatic one seems to have been made for pedagogical purposes.
The conversion of this balance to an electrostatic one seems to have been made for pedagogical purposes.
