Gold-leaf type electroscope by Société Centrale de Produits Chimiques

Background on gold-leaf type electroscope by Société Centrale de Produits Chimiques, Object ID 1994.0125.16
A gold-leaf type electroscope is a device used to detect the presence of electric charge on a body and its relative amount. The electroscope is usually constructed with a metal plate or sphere at the top of a metal post (electrode) with thin foil leaves (e.g., gold) hanging from the bottom of the post. When the electrode is charged by induction or by contact, the leaves acquire similar electric charges and repel each other due to the Coulomb force. Their separation is a direct indication of the net charge stored on them. To protect the gold leaves from drafts of air they are typically enclosed in a glass bottle or glass-walled chamber, usually open at the bottom and mounted over a conductive base. Often there are grounded metal plates or foil strips in the bottle flanking the gold leaves on either side. These are a safety measure; if an excessive charge is applied to the delicate gold leaves, they will touch the grounding plates and discharge before tearing. They also capture charge leaking through the air that could accumulate on the glass walls, and increase the sensitivity of the instrument. Object ID no. 1994.0125.15 is example of a less expensive, gold-leaf type electroscope (refer to object on the left in the image).
Detailed description of object ID no. 1994.0125.16
Gold-leaf type electroscope by Société Centrale de Produits Chimiques
(All accompanying photographs provided by donor, Prof. Herbert Clark, Rensselaer Polytechnic Institute.)
(Refer to the object on the right in the image.)
A circular base supports a cylindrical pedestal, atop which is a cylindrical metal chamber, its axis horizontal, with circular glass end-windows. A section of the pedestal opens out on a pivot, this section supporting a polished metal disc. When in the closed position, this disc is at the bottom of the space in the pedestal, beneath an axial vertical metal rod supported by an amber insulator.
At the top of the pedestal is a knurled ring that clamps the chamber above to the pedestal. The chamber contains a vertical plate to which is attached a strip of silvery foil. The plate is supported from below by a bracket attached to the vertical rod passing through the amber insulator at the bottom of the chamber. (Loosening a small thumbscrew on the bracket presumably allows it to be removed from the vertical rod.)
On the back of the vertical plate (opposite the side with the foil) is a spring-like metal strip, against which presses a pin passing through the wall of the chamber, through a cylinder of what is probably insulting material. There is a knurled knob on a threaded rod extending out from the cylinder. The function of this assembly is not clear – perhaps it is for grounding the foil.
On the opposite side of the chamber is a sleeve through which passes a sliding square rod bearing on its inner end a polished plate parallel to that bearing the foil. When the rod is pushed in, the plate covers and protects the foil. When the instrument is in use, the rod is probably withdrawn to expose the foil and act as a safety ground.
At the top of the chamber is a small cylindrical fitting with a threaded stud atop it. Just inside each of the glass windows is a wire mesh screen. In one of these two screens is a circular opening; on the outside face of the adjacent window is engraved a mark (x inside circle). The bezel of each window can be unscrewed from the chamber.
Attached to the chamber, below the insulator with the knurled knob, is a glass bulb, empty, with a wide mouth opening into the chamber. A knurled ring on its neck suggests that it could be unscrewed. Perhaps the bulb was intended to hold a desiccant.
Currently not on view
Object Name
electroscope, gold-leaf type
date made
early 20th century
Société Centrale de Produits Chimiques
Physical Description
glass (overall material)
velvet (box material)
cloth (box material)
metal (spanner material)
wood (box material)
metal (overall material)
electroscope overall: 21.6 cm x 13.8 cm x 11.6 cm; 8 1/2 in x 5 7/16 in x 4 9/16 in
box: 9 3/8 in x 6 1/2 in x 6 5/8 in; 23.8125 cm x 16.51 cm x 16.8275 cm
ID Number
accession number
catalog number
Science & Scientific Instruments
See more items in
Medicine and Science: Modern Physics
Science & Mathematics
Measuring & Mapping
Modern Physics
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
Rensselaer Polytechnic Institute. Department of Chemistry
Additional Media

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