Weston cells

Weston cell A widely used standard cell... 

Mercury is extensively used in various pieces of scientific apparatus, such as thermometers, barometers, high vacuum pumps, mercury lamps, standard cells (for example the Weston cell), and so on. The metal is used as the cathode in the Kellner-Solvay cell (p. 130). 

Wentworth process Weston cell Wet air oxidation Wet ball mill Wet-end additives Wet etching Wetfastness Wet grinding... 

Ideally a standard cell is constmcted simply and is characterized by a high constancy of emf, a low temperature coefficient of emf, and an emf close to one volt. The Weston cell, which uses a standard cadmium sulfate electrolyte and electrodes of cadmium amalgam and a paste of mercury and mercurous sulfate, essentially meets these conditions. The voltage of the cell is 1.0183 V at 20°C. The a-c Josephson effect, which relates the frequency of a superconducting oscillator to the potential difference between two superconducting components, is used by NIST to maintain the unit of emf. The definition of the volt, however, remains as the Q/A derivation described. 

Cadmium sulfate solutions are used ia the standard Weston cell and as electrolytes ia electroplatiag as alternatives to cyanide baths. Other uses iaclude phosphors and as a nematocide. 

In potentiometric measurements of emf, it is necessary to have a cell where emf is constant with time and is exactly known. For this purpose, a standard Weston cell is commonly employed. A diagram of a simplified potentiometer is shown in Figure 6.9. It consists of a... 

Another galvanic cell of highly practical and theoretical importance is the so-called standard cell (see Section 2.2.2), use of which has to be made as a calibration standard in non-faradaic potentiometry. For this purpose, the saturated Weston cell is the most accepted as its emf is reproducible, precisely known, only slightly temperature dependent in the region around 25° C (1.01832 V) and insensitive to unexpected current flows, if any. 

The mostly used Weston cell consists of mercurous sulphate and cadmium amalgam electrodes ... 

Westheimer, Frank, 16 727, 741 Westinghouse AP600 reactor, 17 595 Westinghouse Bettis Laboratory, 17 573 Westinghouse Model 412 pressurized water reactor, 17 574-577 West Nile encephalitis, 14 338 West Nile virus (WNV), 3 135, 137 antiviral therapy, 3 165-168 infection process, 3 164-165 Weston cell, 15 750 Wet adhesion... 

The Weston cell shown here is a stable voltage standard formerly used in potentiometers. (The potentiometer compares an unknown voltage with that of the standard. In contrast with the conditions of this problem, very little current may be drawn from the cell if it is to be an accurate voltage standard.)... 

A saturated Weston cell containing excess solid CdS04 Is a more precise voltage standard than the unsaturated cell but is more sensitive to temperature and mechanical shock and cannot be easily incorporated into portable equipment. 

Weston cell A stable voltage source based on the reaction Cd(.v) + HgS04(aq) CdS04(atf) + Hg(/). It was formerly used to standardize a potentiometer. 

CdO is used in connection with the stabilization of poly(vinyl chloride). This is discussed below in more detail. It also finds application in modifying the thermal properties of teflon and some rubbers. CdS is used in some smoke detectors, in lasers and in phosphors. The cadmium(II) halides are important as catalysts and are also used in pyrotechnics. Cadmium borates of the general type (Cd0)x(B203), are also used as phosphors. CdS04 is employed in the Weston cell, which is important as a voltage standard.137... 

The unsaturated Weston cell (saturated at 4°C with CdS04) is more rugged and has a negligible temperature coefficient. These cells are the ones usually... 

The Weston cell is the most suitable standard cell for measuring electromotive forces because of its excellent reproducibility it is shown in diagrammatical form in Fig. 9. 

When tho potential on the cell terminals is higher than the electromotive force of the cell the process proceeds in a reverse direction The surplus of solid salts (Hg2S04 and CdS04.8/3 HgO) ensures that the solutions at both electrodes are always saturated, so that the electrode potentials are constant at a constant temperature. The dependence on the temperature of the EMF of the described Weston cell is expressed by the equation ... 

Standard cell — An electrochemical cell composed of two - half-cells containing electrodes built according to standard (normal) conditions. Frequently the term is also used for electrochemical cells showing a well-defined, reproducible, and stable cell voltage suitable for calibration purposes (- Weston cell, - Clark cell). 

Standard Cell. The electrochemical cell used as a voltage standard is the Weston cell, shown in Fig. 13. The voltage of this cell changes only slightly with temperature and is given in absolute volts by... 

Operational amplifier circuit to deliver current at a standard Weston cell voltage. 

The cells were of the type used extensively in this laboratory for earlier studies. The essential features of the cell design have been set forth elsewhere (16). The emf was measured with a Hewlett-Packard digital voltmeter, Model 3460, checked occasionally against laboratory standards consisting of two saturated Weston cells maintained at a controlled temperature. 

Although the so-called saturatedWeston cell, containing a saturated solution of cadmium sulfate, is the ultimate standard for E.M.F. measurement, a secondary standard for general laboratory use has been recommended this is the unsaturated Weston cell, which has an even smaller temperature coefficient than the saturated cell. The form of unsaturated cell generally employed contains a solution which has been saturated at 4 c., so that it is unsaturated at room temperatures its temperature coefficient is so small as to be negligible for all ordinary purposes and its e.m.p. may be taken as 1.0186 volt. ... 

It is important to note that the mercury electrode of a commercial Weston cell is always marked positive while the cadmium amalgam electrode is marked negative,... 

Usually, after a reaction is about 98% complete, a current of about 0.1 of the normal value is used. In the apparatus developed for coulometry of high accuracy, the voltage of the regulated power supply seldom changes by more than 0.001% in a day, the current is accurately measurable through the use of a standard resistor (known to better than 1 ppm) of high precision, and adjustment of the iR drop is made equal to that of a Weston cell. The time can be measured to an accuracy of 1 ppm or better. ... 

Use Chemical (admixed with sulfuric acid as a catalyst, in oxidation of naphthalene to phthalic acid), batteries (Clark cell, Weston cell). 

Weston cell. An electrical cell used as a standard that consists of an amalgamated cadmium anode covered with crystals of cadmium sulfate dipping into a saturated solution of the salt, and a mercury cathode covered with solid mercury sulfate. 

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