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Weston Cell

 
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The Weston cell, invented by Edward Weston
Edward Weston (chemist)

Edward Weston was an English chemist noted for his achievements in electroplating and his development of the electrochemical cell, named the Weston cell, for the voltage standard....
 in 1893, is a wet-chemical cell
Wet cell

A wet cell is a galvanic electrochemical cell with a liquid electrolyte. A dry cell, on the other hand, is a cell with a pasty electrolyte. Wet cells were a precursor to dry cells and are commonly used as a learning tool for electrochemistry....
 that produces a highly stable voltage
Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
 suitable as a laboratory standard for calibration
Calibration

Calibration is the validation of specific measurement techniques and equipment. At the simplest level, calibration is a comparison between measurements-one of known magnitude or correctness made or set with one device and another measurement made in as similar a way as possible with a second device....
 of voltmeter
Voltmeter

A voltmeter is an instrument used for measuring the electrical potential difference between two points in an electric circuit. Analog voltmeters move a pointer across a scale in proportion to the voltage of the circuit; digital voltmeters give a numerical display of voltage by use of an analog to digital converter....
s. It was adopted as the International Standard for EMF
Electromotive force

Electromotive force is a term used to characterize electrical devices, such as voltaic cells, Thermoelectric effects, electrical generators and transformers, and even resistors....
 in 1911.

Chemistry
The anode
Anode

An anode is an electrode through which electric charge flows into a polarized electrical device. Mnemonic: ACID . Electrons flow in the opposite direction to the positive electric current....
 is an amalgam
Amalgam

Amalgam may refer to:* Amalgam , mercury alloy* Amalgam , material of "silver" tooth fillings* Amalgam Comics, publisher* Amalgam, Gauteng, South Africa...
 of cadmium
Cadmium

Cadmium is a chemical element with the symbol Cd and atomic number 48. A relatively abundant , soft, bluish-white, transition metal, cadmium is known to cause cancer and occurs with zinc ores....
 with mercury
Mercury (element)

Mercury , also called quicksilver or hydrargyrum , is a chemical element with the symbol Hg and atomic number 80. A heavy, silvery d-block metal, mercury is one of six elements that are liquid at or near room temperature and pressure....
, the cathode
Cathode

A cathode is an electrode through which electric charge flows out of a polarized electrical device. Mnemonic: CCD .From an electrochemical point of view, positively charged ion invariably move toward the cathode and/or negatively charged ion move away from it to balance the electrons arriving from external circuitry....
 is of pure mercury, the electrolyte
Electrolyte

An electrolyte is any substance containing free ions that behaves as an electrical conductor medium. Because they generally consist of ions in solution, electrolytes are also known as ionic solutions, but molten electrolytes and solid electrolytes are also possible....
 is a solution
Solution

In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent....
 of cadmium sulfate
Cadmium sulfate

Cadmium sulfate is used widely in industries for the electroplating of cadmium in electronic circuits. It is also known as the hydrated form, CdSO4.8/3H2O....
 and the depolarizer
Depolarizer

A depolarizer or depolariser is a substance used in an electrochemical cell, which takes up electrons during discharging the cell; therefore, it is always an oxidizing agent....
 is a paste of mercurous sulfate.

As shown in the illustration, the cell is set up in an H-shaped glass vessel with the cadmium amalgam in one leg and the pure mercury in the other.






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Encyclopedia


Westoncell
The Weston cell, invented by Edward Weston
Edward Weston (chemist)

Edward Weston was an English chemist noted for his achievements in electroplating and his development of the electrochemical cell, named the Weston cell, for the voltage standard....
 in 1893, is a wet-chemical cell
Wet cell

A wet cell is a galvanic electrochemical cell with a liquid electrolyte. A dry cell, on the other hand, is a cell with a pasty electrolyte. Wet cells were a precursor to dry cells and are commonly used as a learning tool for electrochemistry....
 that produces a highly stable voltage
Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
 suitable as a laboratory standard for calibration
Calibration

Calibration is the validation of specific measurement techniques and equipment. At the simplest level, calibration is a comparison between measurements-one of known magnitude or correctness made or set with one device and another measurement made in as similar a way as possible with a second device....
 of voltmeter
Voltmeter

A voltmeter is an instrument used for measuring the electrical potential difference between two points in an electric circuit. Analog voltmeters move a pointer across a scale in proportion to the voltage of the circuit; digital voltmeters give a numerical display of voltage by use of an analog to digital converter....
s. It was adopted as the International Standard for EMF
Electromotive force

Electromotive force is a term used to characterize electrical devices, such as voltaic cells, Thermoelectric effects, electrical generators and transformers, and even resistors....
 in 1911.

Chemistry


The anode
Anode

An anode is an electrode through which electric charge flows into a polarized electrical device. Mnemonic: ACID . Electrons flow in the opposite direction to the positive electric current....
 is an amalgam
Amalgam

Amalgam may refer to:* Amalgam , mercury alloy* Amalgam , material of "silver" tooth fillings* Amalgam Comics, publisher* Amalgam, Gauteng, South Africa...
 of cadmium
Cadmium

Cadmium is a chemical element with the symbol Cd and atomic number 48. A relatively abundant , soft, bluish-white, transition metal, cadmium is known to cause cancer and occurs with zinc ores....
 with mercury
Mercury (element)

Mercury , also called quicksilver or hydrargyrum , is a chemical element with the symbol Hg and atomic number 80. A heavy, silvery d-block metal, mercury is one of six elements that are liquid at or near room temperature and pressure....
, the cathode
Cathode

A cathode is an electrode through which electric charge flows out of a polarized electrical device. Mnemonic: CCD .From an electrochemical point of view, positively charged ion invariably move toward the cathode and/or negatively charged ion move away from it to balance the electrons arriving from external circuitry....
 is of pure mercury, the electrolyte
Electrolyte

An electrolyte is any substance containing free ions that behaves as an electrical conductor medium. Because they generally consist of ions in solution, electrolytes are also known as ionic solutions, but molten electrolytes and solid electrolytes are also possible....
 is a solution
Solution

In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent....
 of cadmium sulfate
Cadmium sulfate

Cadmium sulfate is used widely in industries for the electroplating of cadmium in electronic circuits. It is also known as the hydrated form, CdSO4.8/3H2O....
 and the depolarizer
Depolarizer

A depolarizer or depolariser is a substance used in an electrochemical cell, which takes up electrons during discharging the cell; therefore, it is always an oxidizing agent....
 is a paste of mercurous sulfate.

As shown in the illustration, the cell is set up in an H-shaped glass vessel with the cadmium amalgam in one leg and the pure mercury in the other. Electrical connections to the cadmium amalgam and the mercury are made by platinum
Platinum

Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is in Group 10 of the periodic table of elements....
 wires fused through the lower ends of the legs.

Characteristics


The original design was a saturated cadmium cell producing a convenient 1.0183 Volt
Volt

The volt is the SI SI derived unit of electric potential difference or electromotive force, commonly known as voltage. It is named in honor of the Lombard physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery ....
 reference and had the advantage of having a lower temperature coefficient
Temperature coefficient

The temperature coefficient is the relative change of a physical property when the temperature is changed by 1 Kelvin.In the following formula, let R be the physical property to be measured and T be the temperature at which the property is measured....
 than the previously used Clark cell
Clark cell

The Clark cell, invented by English engineer Josiah Latimer Clark in 1873, is a wet cell that produces a highly stable voltage usable as alaboratory standard....
. (Reference cells must be applied in such a way that no current is drawn from them.)

The temperature coefficient can be reduced by shifting to an unsaturated design, the predominant type today. However, an unsaturated cell's output decreases by some 80 microvolts per year, which is compensated by periodical calibration against a saturated cell.

Patent


See also


  • Primary cell terminology
    Primary cell terminology

    Primary cell terminology offers much scope for confusion. When a primary cell is in use there are two circuits:* The external circuit, e.g. a lamp connected by wires to the cell terminals...


Sources


  • Practical Electricity by W. E. Ayrton and T. Mather, published by Cassell and Company, London, 1911, pp 198-203


External links