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Graduation tower
(726 words)

Graduation towers were used starting in the mid-16th century to raise the concentration of saline solution used in the extraction of salt (sole) before reaching boiling point in order to save energy and expense.

The optimal saturation of sodium chloride in water is 26.4% at 20°C; at basic atmospheric pressure, the boiling point is 109°C. In most European salt works, however, the salt concentration at source was below 5%, and a few were only at 1-2%, for example at Unna/Westphalia. So, salt works with 1% brines required thirty times as much energy to produce the same amount of sa…

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Fessner, Michael, “Graduation tower”, in: Encyclopedia of Early Modern History Online, Editors of the English edition: Graeme Dunphy, Andrew Gow. Original German Edition: Enzyklopädie der Neuzeit. Im Auftrag des Kulturwissenschaftlichen Instituts (Essen) und in Verbindung mit den Fachherausgebern herausgegeben von Friedrich Jaeger. Copyright © J.B. Metzlersche Verlagsbuchhandlung und Carl Ernst Poeschel Verlag GmbH 2005–2012. Consulted online on 24 July 2019 <http://dx.doi.org/10.1163/2352-0272_emho_SIM_020394>
First published online: 2015
First print edition: 20180915



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