Lime
Calcium oxide (CaO), more commonly known as lime or quicklime, has been studied by scholars as far back as the pre-Christian era. In his book Historia Naturalis, for example, Pliny the Elder discussed the preparation, properties, and uses of lime. Probably the first scientific paper on the substance was Dr. Joseph Black's "Experiments Upon Magnesia, Alba, Quick-lime, and Some Other Alkaline Substances," written in 1755.
Lime does not occur naturally since it reacts so readily with water (to form hydrated lime) and carbon dioxide (to form limestone). It is synthetically produced in very large quantities by the heating of limestone. For many years, calcium oxide has ranked among the top 10 chemicals in the United States in terms of production. Other common names by which the compound is known include burnt lime, unslaked lime, fluxing lime, and calx.
In its pure form, calcium oxide occurs as white crystals, white or gray lumps, or a white granular powder. It has a very high melting point of 4,662°F (2,572°C) and a boiling point of 5,162°F (2,850°C). It dissolves in and reacts with water to form calcium hydroxide and is soluble in acids and some organic solvents.
Like other calcium compounds, calcium oxide is used for many construction purposes, as in the manufacture of bricks, mortar, plaster, and stucco. Its high melting point makes it attractive as a refractory material, as in the lining of furnaces. The compound is also used in the manufacture of various types of glass. Common soda-lime glass, for example, contains about 12% calcium oxide, while high-melting aluminosilicate glass contains about 20% calcium oxide. One of the new forms of glass used to coat surgical implants contains an even higher ratio of calcium oxide, about 24% of the compound.
Lime is also used in the production of pulp and paper, the removal of hair from animal hides, clarifying cane and beet sugar, in poultry feeds, and as a drilling fluid.
In 1816, Thomas Drummond invented limelight, and in 1825 its first use was during a survey of Ireland. Drummond's early limelight was based on a torch that burned hydrogen and oxygen, which had been developed by Robert Hare (1781-1858), an American chemist. Although limelight was considered for lighthouse applications, the cost of production was too high. In 1837, limelight found its niche in the theater, where it was used not only to spotlight actors but also to create realistic special effects such as moonlight on a river or clouds moving through the sky. The light was produced by pointing a hot torch at a solid block of lime (calcium oxide). When heated, the lime gave off a bright, soft white light that was easy to focus on a small area by using a mirror as a reflector. However, limelight had a major disadvantage; it required constant attention by a stagehand to keep turning the block of lime and tending the gas torch. In the late 1800s, limelight began to be replaced by electric arc spotlights. However, its name has lived on; we still speak today of "basking in the limelight" of popularity or attention.
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