Weston cell

Westoncell Volt

Weston cell - Hanford B Reactor - Benton County, Washington

Standart cell

Weston Cell

The Weston cell is a type of wet cell battery that was invented by Edward Weston in 1893. It is a chemical battery that produces a highly stable voltage suitable for use as a standard cell in laboratory measurements. The Weston cell's notable feature is its ability to maintain a constant voltage over time, making it an essential tool for the calibration of voltmeters and other voltage measuring equipment.

History

Edward Weston, an English engineer and chemist who moved to the United States, developed the Weston cell in the late 19th century. His invention was aimed at improving the stability and reliability of electrochemical cells used as voltage standards. The Weston cell was widely adopted as a standard of electromotive force (EMF) after its introduction due to its superior stability and reproducibility compared to other cells of the time.

Design and Operation

The Weston cell consists of a cathode made of mercury and a anode made of cadmium amalgam. The electrolyte is a saturated solution of cadmium sulfate and mercury sulfate in water, with a paste of mercury sulfate at the bottom to increase the cell's stability and lifespan. The cell operates at a standard voltage of approximately 1.0186 volts at 20°C, which is remarkably consistent over time and under various conditions.

The design of the Weston cell minimizes changes in voltage by carefully controlling the chemical composition and physical conditions within the cell. The presence of the mercury sulfate paste ensures that the mercury does not dissolve into the solution, which would otherwise alter the cell's voltage.

Types of Weston Cells

There are two main types of Weston cells: the saturated cell and the unsaturated cell. The saturated Weston cell operates at a slightly higher voltage and is more stable, making it suitable for use as a primary standard. The unsaturated cell, while still precise, is more affected by temperature changes and is generally used where less stringent standards are acceptable.

Applications

The Weston cell was historically used as a standard for calibrating electrical measurement devices due to its stable voltage output. It served as the primary standard for voltage in many national laboratories and was used in the definition of the volt until the adoption of the Josephson voltage standard, based on quantum electrical phenomena, which offered even greater precision and stability.

Legacy

Although the Weston cell has been largely replaced by more modern standards for practical applications, its invention marked a significant milestone in the development of electrical measurement techniques. It remains a topic of interest in the history of science and technology, illustrating the evolution of measurement standards and the importance of precision in scientific research.

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