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Encyclopedia > Desiccant

A dessicant is a hygroscopic substance that induces or sustains a state of dryness (desiccation) in its local vicinity in a moderately-well sealed container. A desiccant is a substance that adsorbs moisture from the air. ... A hygroscopic substance is a substance that absorbs water readily from its surroundings. ... Desiccation is the state of extreme dryness, or the process of extreme drying. ...


Commonly encountered pre-packaged desiccants are solids, and work through absorbtion or adsorption of water, or a combination of the two. Desiccants for specialised purposes may be in forms other than solid, and may work through other principles, such as chemical bonding of water molecules. Absorption, in chemistry, is a physical or chemical phenomenon or a process in which atoms, molecules, or ions enter some bulk phase - gas, liquid or solid material. ... Adsorption is a process that occurs when a gas or liquid or solute (called adsorbate) accumulates on the surface of a solid or more rarely a liquid (adsorbent), forming a molecular or atomic film (adsorbate). ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ...


Pre-packaged desiccant is most commonly used to remove humidity that would normally degrade or even destroy products sensitive to moisture. Silica gel, calcium sulfate, montmorillonite clay, and molecular sieves are commonly used as desiccants. This article or section is not written in the formal tone expected of an encyclopedia article. ... Beads of silica gel Silica gel is a granular, porous form of silica made synthetically from sodium silicate. ... Calcium sulfate is a common laboratory and industrial chemical. ... A sample of montmorillonite Montmorillonite is a very soft phyllosilicate mineral that typically forms in microscopic crystals, forming a clay. ... The Gay Head cliffs in Marthas Vineyard are made almost entirely of clay. ... A molecular sieve is a material containing tiny pores of a precise and uniform size that is used as an adsorbent for gases and liquids. ...


Rice is a common "low-tech" alternative, frequently used for example in salt-shakers to maintain granularity of table-salt for effective pouring or shaking. Rice, however, is not a good general purpose desiccant since, unless immersed in an organism-hostile environment like pure salt, over time may be eaten by creatures that might in turn pollute the product that is being preserved. Salt itself is another effective desiccant, used for millenia in preparation of dried foodstuffs. Species Oryza glaberrima Oryza sativa Brown basmati rice Terrace of paddy fields in Yunnan Province, southern China. ... The term low-technology is a description of those crafts and tools whose inception (typically) predates the Industrial Revolution. ... A whole potato, sliced pieces (right), and dried sliced pieces (left) Drying is a method of food preservation that works by removing water from the food, which prevents the growth of microorganisms and decay. ...

Contents

Toxicity

A desiccant may be chosen for a particular task based not only on its effectiveness at drying, but also perhaps for any natural antibiotic/fungicidal/pesticidal effect, or for a lack of harmful effect on humans -- for instance salt has a natural antibiotic and anti-fungal effect and is not harmful to humans when consumed in moderate quantities, hence its popular use a drying agent in preparation of dried foods. Staphylococcus aureus - Antibiotics test plate. ... A Fungicide is one of three main methods of pest control- chemical control of fungi in this case. ... A cropduster spreading pesticide. ...


Desiccants may also incorporate secondary substances in order to achieve such antibiotic etc properties. These may be mineral, synthetic, or herbal in origin, and vary in toxicity toward humans. Always pay close attention to the handling instructions of pre-packaged desiccants you encounter, although it is not necessary to strictly obey the commonly-encountered direction to "discard" or "throw away". The direction is meant to indicate that the desiccant is not a significant part of the item, and in food, that the desiccant is not meant for consumption, but may be put aside at preparation time. You might choose to recycle the desiccant for use in storing your own goods, be they food items or otherwise. Minerals are natural compounds formed through geological processes. ... Generally, synthetic means pertaining to synthesis, i. ... An herbal is a book, often illustrated, that describes the appearance, medical properties, and other characteristics of plants used in herbal medicine. ...


Chemical reactivity

Because of their common use in preservation, usually it is desirable for a desiccant to be substantially chemically stable or chemically inert, and a number of useful desiccants with this property have been identified and are in common use, such as silica gel, chalk- and clay-based desiccants. In English, to be inert is to be in a state of doing little or nothing. ...


Performance efficiency

One measure of desiccant efficiency is the ratio (or percentage) of water storeable in the desiccant, relative to the mass of desiccant (ie weight). The percent sign. ... Unsolved problems in physics: What causes anything to have mass? The U.S. National Prototype Kilogram, which currently serves as the primary standard for measuring mass in the U.S. Mass is the property of a physical object that quantifies the amount of matter and energy it is equivalent to. ... A spring scale measures the weight of an object In the physical sciences, weight is a measurement of the gravitational force acting on an object. ...


Another measure is the residual relative humidity of the air or other fluid being dried. This does not adequately cite its references or sources. ...


The performance of any desiccant varies with temperature and both relative and absolute humidity. To some extent the performance can be described, but most commonly the final choice of which desiccant best suits a given situation, and how much of it to use, and in what form, is made based on testing and experience. Fig. ... Absolute humidity is the mass of water vapor in a given volume of air or gas, expressed by weight and usually measured in grams per cubic meter, though grains per cubic foot has also been used in the United States. ...


Coloured saturation indicators

Often some sort of humidity indicator is included in the desiccant to show, by color changes, the degree of water-saturation of the desiccant. One commonly used indicator 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)6]Cl2. This article or section is not written in the formal tone expected of an encyclopedia article. ... Cobalt(II) chloride (CoCl2) is a chemical compound composed of cobalt and chlorine. ... As a general term, a substance is said to be anhydrous if it contains no water. ...


Most useful desiccants can be recycled by thermally-induced drying, for example in a conventional kitchen oven. The international symbol for recycling. ... Example of a thermal column between the ground and a cumulus This article is about the atmospheric phenomenon. ... Oven depicted in a painting by Millet An oven is an enclosed compartment for heating, baking or drying. ...


Drying of solvents

Desiccants are also used to dry solvents, typically used for moisture free reactions (e.g. the Grignard reaction). While various dessicants are used in a variety of ways, the method generally involves stirrying the desired solvent with the drying agent. A substance is soluble in a fluid if it dissolves in the fluid. ... The Grignard reaction is an organometallic chemical reaction involving alkyl- or aryl-magnesium halides, also called Grignard reagents, with electrophiles. ...


Often, the drying agent will react with moisture to form an insoluble solid in the solvent being dehydrated, thus the precipitate can be removed by filtration. For more demanding applications, requiring very pure, anhydrous solvents a distillation rig is used to remove moisture and other impurities simultaneously. Laboratory distillation set-up using, without a fractionating column 1: Heat source 2: Still pot 3: Still head 4: Thermometer/Boiling point temperature 5: Condenser 6: Cooling water in 7: Cooling water out 8: Distillate/receiving flask 9: Vacuum/gas inlet 10: Still receiver 11: Heat control 12: Stirrer speed...


See also

A desiccant is a substance that absorbs water. ... Hygroscopy is the ability of a substance to attract water molecules from the surrounding environment through either absorption or adsorption. ...

External links

  • Desiccant info
  • Latest US desiccants patents information.
  • A Desiccant Requirements Calculator
  • Mummification of an Apple
  • Combating Moisture and Humidity in Nutraceutical Packaging
  • Desiccant Selection Guide
  • True potato seed drying over rice

  Results from FactBites:
 
Appropriate desiccant selection can improve product (IVDT archive, Jun 02) (2882 words)
Desiccant canisters are considered the gold standard among the desiccants used in the pharmaceutical industry.
Desiccant cap inserts are used in conjunction with screw-on caps for rigid containers.
Absorption capacity is measured by exposing the desiccant to specified, static conditions and observing its weight increase, which is given as a percentage of the desiccant weight.
Desiccation - Wikipedia, the free encyclopedia (343 words)
Desiccation is the state of extreme dryness, or the process of extreme drying.
A desiccant is a substance that adsorbs water.
Desiccated coconut is the dried, finely shredded flesh of the coconut, much used in cooking desserts.
  More results at FactBites »

 
 

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