Steelmaking technique that for most of the 20th century accounted for most steel made in the world. William Siemens made steel from pig iron in a reverberatory furnace of his design in 1867. The same year the French manufacturer Pierre-Émile Martin (1824–1915) used the idea to produce steel by melting wrought iron with steel scrap. Siemens used the waste heat given off by the furnace: he directed the fumes from the furnace through a brick checkerwork, heating it to a high temperature, and then used the same path to introduce air into the furnace; the preheated air significantly increased the flame temperature. The open-hearth process furnace (which replaced the Bessemer process) has itself been replaced in most industrialized countries by the basic oxygen process and the electric furnace. Seealso reverberatory furnace.
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In archaeology, a hearth is a firepit or other fireplace feature of any period. Hearths are common features of many eras going back to prehistoric campsites, and may be either lined with a wide range of materials or left unlined. Hearths were used for cooking, heating, and processing of some stone, wood, faunal, and floral deform or disperse hearth features, making them difficult to identify without careful study.
Lined hearths are easily identified by the presence of fire-cracked rock, often created when the heat from the fires inside the hearths chemically altered and cracked the stone. Often present are fragmented fish and animal bones, carbonized shell, charcoal, ash, and other waste products, all embedded in a sequence of soil that has been deposited atop the hearth. Unlined hearths, which are less easily identified, may also include these materials. Because of the organic nature of most of these items, they can be used to pinpoint the date the hearth was last used via the process of radiocarbon dating. Although carbon dates can be negatively affected if the users of the hearth burned old wood or coal, the process is typically quite reliable. This was the most common way to heat interior spaces and for cooking in cool seasons.
In England, a tax on hearths was introduced on 19 May 1662. Householders were required to pay a charge of two shillings per annum for each hearth, with half the payment due at Michaelmas and half at Lady Day. Exemptions to the tax were granted, to those in receipt of poor relief, those whose houses were worth less than 20 shillings a year and those who paid neither church nor poor rates. Also exempt were charitable institutions such as schools and almshouses, and industrial hearths with the exception of smiths' forges and bakers' ovens. The returns were lodged with the Clerk of the Peace between 1662 and 1688.
A revision of the Act in 1664 made the tax payable by all who had more than two chimneys
Hearth tax records are important to local historians as they provide an indication of the size of each assessed house at the time. The numbers of hearths are generally proportional to the size of the house. The assessments can be used to indicate the numbers and local distribution of larger and smaller houses. Not every room had a hearth, and not all houses of the same size had exactly the same number of hearths, so they are not an exact measure of house size. Roehampton University has an ongoing project which places hearth tax data in a national framework by providing a series of standard bands of wealth applicable to each county and city.
Published lists are available of many returns and the original documents are in the Public Record Office. The most informative returns, many of which have been published, occur between 1662-1666 and 1669-1674.