Wedgwood scale

The Wedgwood scale is a temperature scale for higher temperatures, such as occur for example in the porcelain or metal fabrication. It is named after the English entrepreneur Josiah Wedgwood, who proposed it in 1782.

Scale

From Wedgwood was stated that the zero point of his scale is converted at 581 ° C. This is the temperature at he noted first weak redness. Each degree Wedgwood should then correspond to a temperature increase of 72 ° C. Wedgwood are still some melting points of metals as compared to values ​​, copper 27 °, 28 ° silver, gold and bronze 32 ° 21 °. Guyton de Morveau corrected later both the starting point and the conversion degree steps. In de Morveau results for the starting point, a value of 270 ° and each degree Wedgwood is only 34 ° C.

Method

Wedgwood used for its measurement method, the decrease in volume of sound when burning. He used small clay cylinder with a diameter of 0.5 inches, always the same origin and composition. These clay cylinders were now exposed to the environment to be measured and, after cooling, the decrease in the diameter was determined. However, since the decrease is small, the exact determination is difficult. Wedgwood also developed a simple device to easily read the temperature can, this is often called Wedgwood pyrometer. Two metal strips were easily fixed V-shape on a metal sheet. At the wider end of the spacer is 0.5 inch, and thus just large enough for an unfired clay cylinder, while at the lower end, the distance is only 0.3 inches. Now on the whole length 240 marks are registered. To be measured clay cylinder you can now slip into the converging rails and reads from where the cylinder gets stuck.

History

The measurement with a mercury thermometer is just below the boiling point of mercury, that is from 350 ° C, is possible. Higher temperatures could not be determined for a long time. The china manufacturer Josiah Wedgwood developed now for determining the firing temperature, a measurement method and published the method in 1782. The method has been used by many scientists and also in industrial technology, although the scale by the faulty comparison with the other temperature scales was completely inflated values ​​. With the invention of the platinum pyrometer by John Frederic Daniell in 1830 and the use of thermocouples for temperature measurement, the procedure was not used.

Sometimes even the Seger cones are used for temperature control. This does not change through the sintering of the sound, but they fall together by partial melting.