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Desiccator
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{{Short description|Sealable enclosures containing desiccants to preserve moisture-sensitive items}} {{for|dry boxes and cabinets|dry box}} [[File:Desiccator.jpg|thumb|right|A '''vacuum desiccator''' (left - note the stopcock which allows a vacuum to be applied), and a '''desiccator''' (right). The blue [[silica gel]] in the space below the platform is used as the [[desiccant]].]] '''Desiccators''' are sealable enclosures containing [[desiccant]]s used for preserving [[moisture]]-sensitive items such as [[cobalt chloride paper]] for another use. A common use for desiccators is to protect chemicals which are [[hygroscopic]] or which react with water from [[humidity]]. The contents of desiccators are exposed to atmospheric moisture whenever the desiccators are opened. It also requires some time to achieve a low humidity. Hence they are not appropriate for storing chemicals which react quickly or violently with atmospheric moisture such as the alkali metals; a [[glovebox]] or [[Schlenk line|Schlenk]]-type apparatus may be more suitable for these purposes. Desiccators are sometimes used to remove traces of water from an almost-dry sample. Where a desiccator alone is unsatisfactory, the sample may be dried at elevated temperature using [[Abderhalden's drying pistol]]. ==Constituents== The lower compartment of the desiccator contains lumps of [[silica gel]], freshly [[calcined]] [[quicklime]], [[Calcium sulfate#Other uses | Drierite]], [[molecular sieve]]s, [[phosphorus pentoxide]], (not as effective) anhydrous [[calcium chloride]], or other [[List of desiccants|desiccant]] to absorb water vapor. The substance needing desiccation is put in the upper compartment, usually on a glazed, perforated ceramic plate. The ground-glass rim of the desiccator lid must be greased with a thin layer of vacuum grease, petroleum jelly or other lubricant to ensure an airtight seal. In order to prevent damage to a desiccator the lid should be carefully slid on and off instead of being directly placed onto the base.<ref name=qa>{{cite book|last=Alexeyev|first=V.|title=Quantitative Analysis|date=April 2000 |publisher=Lightning source Inc.|isbn=0-89875-034-2}}</ref> ==Operation== In laboratory use, the most common desiccators are circular and made of heavy [[glass]]. There is usually a removable platform on which the items to be stored are placed. The desiccant, usually an otherwise-inert solid such as [[silica gel]], fills the space under the platform. Colour changing silica may be used to indicate when it should be refreshed. Indication gels typically change from blue to pink (if the indicator is [[cobalt(II) chloride]]) as they absorb moisture but other colours may be used. A [[stopcock]] may be included to permit the desiccator to be evacuated. Such models are usually known as '''vacuum desiccators'''. When a vacuum is to be applied, it is a common practice to criss-cross the vacuum desiccator with tape, or to place it behind a screen to minimize damage or injury caused by an [[Implosion (mechanical process)|implosion]]. To maintain a good seal, vacuum [[grease (lubricant)|grease]] is usually applied to the [[flange]]s. ==See also== * [[Bell jar]] * [[Desiccation]] * [[Dry box]] ==References== {{Reflist}} {{Containers}} {{Laboratory equipment}} [[Category:Laboratory glassware]] [[Category:Containers]]
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