Kolbe's Electrometer/Electroscope by Leppin & Masche (ca. 1900)
This example of a Kolbe electroscope (or electrometer, if you prefer) was marketed by Leppin & Masche of Berlin. For the most part, it would have been used for classroom demonstrations of electrostatic phenomena. These demonstrations might, or might not, have involved the use of radioactive materials.
The maker's name is stamped on the end of the wooden base: LEPPIN & MASCHE, BERLIN.SA. Leppin & Masche was a German manufacturer of scientific equipment.
The four vertical sides of the chamber are glass, while the top and bottom are sheet metal. The inside of the glass on the right and left sides (not visible in the above photo) is covered with a wire mesh. This mesh "screened" the inside of the electroscope from the effects of static charges on nearby objects and the glass. For this to work, the metal frame and the wire mesh had to be grounded. The brass connector for grounding the electroscope is located on the far right corner of the wooden base (as seen in the top photo). The larger brass knob on the left end of the wooden base was used to level the electroscope.
Rather than employ two gold leaves, like the "classic" Bennet electroscope, the Kolbe electroscope was designed to use a single aluminum leaf. Nevertheless, a gold leaf or a paper leaf could also be used. Unfortunately, our leaf (paper) has fallen to the bottom of the case.
The curved mica scale inside the chamber was employed to measure the deflection of the leaf - it is numbered in degrees: 0 through 90.
Unlike the other Kolbe electroscope in the collection, this one has a horizontal metal rod that penetrates the chamber (from the lower right side as seen in the top photo). The brass ball at the angled end of the rod, the end inside the chamber, can be brought into contact with the ball at the bottom of the vertical supporting rod in order to ground discharge (ground) the leaf.
Just below the condenser plate on the top of the electroscope, you can see a "hooked" wire rod projecting towards the left. In some instruments this device, which served as an electrical terminal, had a metal ball at the end instead of a hook. It projected far enough outward that you could touch it as a way to ground the leaf without touching the Volta plate (figure below right). It also provided a convenient terminal for connecting the electroscope to other electrical equipment (figure below). When the electroscope was not in use, the wire might be connected to the small brass connection on the top of the electroscope case (figure to right).
The figure to the right is from Frick (1907).The other two figures are from a text by Kolbe (1908).
In general, an electrophorus would be used to transfer a charge to the condenser (Volta plate). For an explanation of how an electroscope can be charged and how an electrophorus works, click here.
For more information about the this type of electroscope, refer to the description of the of the Kolbe electroscope marketed by Max Kohl .
Size: ca 9.5" tall. The chamber is 5.5" high 5" wide and 4" deep. The condenser (Volta) plate is ca. 3" in diameter. The wooden base is 10" x 6".
Frick, J. Physikalische Technik, oder Anleitung zu Experimentalvortragen, II. I. 1907.
Kolbe, K. Ein einfaches Elekrometer. Zeitschrift fur den Physikalischen und Chemischen Unterricht. April 1889;153-159.
Kolbe, B. An Introduction to Electricity. Translated by J. Skellon. 1908.
I would like to express my thanks to Jean-François Loude for providing a couple of the above references.
Last updated: 07/25/07
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