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Desiccation cracks in sludge

Centripetal desiccation cracks in the Lower Jurassic Moenave Formation at the St. George Dinosaur Discovery Site at Johnson Farm, southwestern Utah. Note dinosaur footprint in the center.

Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately-well sealed container.

Science

A vacuum desiccator (left) and desiccator (right). Silica gel with cobalt chloride indicator placed in the lower shelf is used as the desiccant.

Desiccator

In science, a desiccator is a heavy glass or plastic container used in practical chemistry for making or keeping small amounts of material very dry. The material is placed on a shelf, and a drying agent or desiccant, such as dry silica gel or anhydrous sodium hydroxide, is placed below the shelf.

Often some sort of humidity indicator is included in the desiccator to show, by color changes, the level of humidity. These indicators are in the form of indicator plugs or indicator cards. The active chemical is cobalt chloride (CoCl₂). Anhydrous cobalt chloride is blue. When it bonds with two water molecules, (CoCl₂•2H₂O), it turns purple. Further hydration results in the pink hexaaquacobalt(II) chloride complex [Co(H₂O)₆²⁺.

Biology and ecology

In biology and ecology, desiccation refers to the drying out of a living organism, such as when aquatic animals are taken out of water, or when plants are exposed to sunlight or drought. Ecologists frequently study and assess various organisms' susceptibility to desiccation.

Broadcasting

In broadcast engineering, a desiccator may be used to pressurize the feedline of a high-power transmitter. Because it carries very high electrical power levels from the transmitter to the antenna, the feedline must have a good dielectric. Because it must also be lightweight so as not to overload the radio tower, air is often used as the dielectric. Since moisture can condense in these lines, desiccated air or nitrogen gas is pumped in. This pressure also keeps water or other dampness from coming in the line at any point along its length.

Desiccation cracks resulting as part of a flood deposit on the Mancos River near Towaoc, Colorado as seen on September 25, 2003.

See also

• List of desiccants
• Hygroscopy
• Mummification

External links

• A Desiccant Requirements Calculator

Wikipedia content modification information:

• This page was last modified on 22 September 2008, at 14:03.

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