The History of Calcium Hydroxide
Limestone is the main ingredient found in, marble, calcite, chalk, seashells, and many other calciferous substances. Limestone is, chemically, calcium carbonate (CaCO₃). If one heats calcium carbonate to elevated temperatures, carbon dioxide gas (CO₂) is driven off, leaving calcium oxide (CaO), also called lime or quicklime, behind. Calcium oxide, combined with water, produces calcium hydroxide (Ca(OH)₂), called hydrated lime or "slaked lime" because it is as if the lime has had its thirst slaked or quenched.
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Historical Uses
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Because it is so readily available and easy to make, calcium hydroxide has been used in many ways, some of them having very early origins. Examples include hair removal, in making Bordeaux Mixture (a fungicide and bactericide), in whitewash, in mortar and plaster, as a flocculent in sewage treatment, in processing corn, and in processing sugarcane.
In Treating Hides
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Removal of hair from hides is often accomplished by one or both of two agencies: lime, which loosens the base of hair follicles; and sulfide, which hydrolyzes the amino groups of glutamine and asparagine.
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In Bordeaux Mixture
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Bordeaux mixture, which dates back to 1860s France, is a combination of 4 pounds of copper sulfate, 4 pounds of slaked lime, and 50 gallons of water. It is especially useful in viticulture.
In Whitewash
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Whitewash at its most basic level is a mixture of slaked lime and water, though other ingredients such as glue, colorants, and powdered chalk may be included. The applied coating is strengthened by the gradual absorption of carbon dioxide by the slaked lime to form calcium carbonate.
Processing Corn to Form Nixtamal
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Dried field corn is boiled and then soaked in water containing slaked lime. This forms masa, which is then used to make tortillas. It is used in Native American and Latin cooking, and improves flavor and the nutritional value of the processed corn.
Sugar Cane
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Slaked lime is used to clean up sugar cane juice prior to its being boiled down into thickened syrup.
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- Photo Credit Image by Flickr.com, courtesy of Josef F. Stuefer
