Tasting oven
A tasting furnace is a furnace that was used by the tasters in the art of tasting to melt down and pretreat ore samples. The test ovens were made of various materials such as fired stone or sheet metal. The dimensions and layout of the ovens were noted by the tasters in their tasters' books.
construction
The test furnaces essentially consisted of four main parts, these were the boiler room, the furnace room, the work room and the annealing or melting room. Refractory materials had to be used for construction. In his Twelve Books of Mining and Metallurgy Agricola describes some of the basic structures of test ovens. In terms of shape, these ovens were either round or square. Brick masonry, clay or iron were used as building materials. A brick stove was a cubit high, a foot wide inside, and a little over a foot deep. An iron plate covered with clay was attached five fingers above the furnace. Above the plate was an opening in the front wall that was five fingers wide and one hand high. There were slots in the plate that were used for ash removal and drafts. Iron tasting ovens consisted of four 1.5-foot long iron rods with the outer walls attached between them. There was an opening in the front wall through which the sample could be introduced. Clay trial ovens were about the same size as iron ovens. They were made from several clay plates. There were four openings on the side walls and on the back wall, each three fingers high and five fingers wide. These openings were used to supply air. There was an opening in the front wall that was 1.5 hands wide. This opening was used to place the sample vessels (chapels) in the oven. The chapels were placed on a slotted clay plate. This plate was reinforced with iron wire for stability. The stove's poke hole was either on the front or the back. The advantage of ovens with a pothole on the back was that the tester wasn't exposed to as much heat. The disadvantage of this construction was that the tester could not set the oven temperature so easily. Brick ovens were stationary, iron or clay ovens were moveable. The ovens were built either high or low.
Types and application
There were basically two types of test ovens, wind ovens and fan ovens. In wind ovens, the fire was supplied with air by the normal draft of air, in fan ovens a bellows was used for artificial air supply. Both types could only be operated for a maximum of three to four hours, after which the grate or the Deupen opening were so heavily clogged with slag that further operation was not possible. The stoves were fired with charcoal , coke or a mixture of both fuels. Both furnace types were roughly equivalent in terms of heating behavior. Wind ovens had the advantage that no second man was needed to operate the bellows. Fan ovens were more advantageous for special cases, e.g. B. a sample had to be heated particularly strongly. In the small test ovens, the samples were heated on small crucibles, so-called test shards. So-called muffles had to be used for larger samples; these test furnaces were called muffle furnaces . If the rising exhaust gases had very high temperatures, they could still be used to operate another furnace. The exhaust gases were then led into the combustion chamber of the second furnace via an exhaust pipe, the so-called Fuchs. In the second furnace, however, only samples with low-viscosity metals could be melted.
Examples of different ovens
Different test furnaces were constructed and operated on the basis of the two basic types. In the laboratory of the University of Clausthal there was a portable coin or fine sample furnace made of sheet iron. The same furnace was used in the Hanover Mint. Trial furnaces with opposing muffles were used in the Paris Mint. In the Freiberger Hütte, coal muffle furnaces were used instead of the solidly bricked test furnaces. A portable tasting oven has been developed by Aikin. This furnace was a forced air furnace in which graphite crucibles were used. These crucibles could also withstand large temperature differences undamaged.
The Englishman David Mushet invented a tasting furnace that was equipped with a pyrometric display. The pyrometric display consisted of a rod directly exposed to the heat of the oven. The rod pressed against a lever with a tip attached to it. This tip moved along an arc of a degree, depending on the temperature.
Individual evidence
- ^ Johann Christoph Stößel (Ed.): Mining dictionary. Chemnitz 1778.
- ↑ New and well-established mineral and mining lexocon. Bey Johann Christoph and Johann David Stößeln, Chemnitz 1743.
- ↑ J. Dumas, Gottl. Aler, Friedr. Engelhart: Handbook of applied chemistry. Fourth volume, by Johann Leonhard Schrag, Nuremberg 1835.
- ↑ a b Georg Agricola: Twelve books on mining and metallurgy. In commission VDI-Verlag GmbH, Berlin
- ↑ a b Bruno Kerl: Metallurgical trial art for use in lectures and for self-study. Published by Arthur Felix, Leipzig 1866.
- ↑ a b c Carl Hartmann: Handbook of probar art on dry ways by P. Berthier. At Johann Leonhard Schrag, Nuremberg 1834.
- ↑ Carl von Scheuchenstuel : IDIOTICON the Austrian mining and metallurgy language. kk court bookseller Wilhelm Braumüller, Vienna 1856.
- ↑ Gabr. Christian. Benj. Busch: Handbook of Inventions. Tenth part, by Johann Friedrich Bäreke, Eisenach 1820.
- ^ Sally Newcomb: The World in a Crucible: Laboratory Practice and Geological Theory at the Beginning of Geology. Boulder, Colo .: Geological Society of America 2009, p. 52, ISBN 978-0-8137-2449-2 , online in the Google book search.