A desiccator is an airtight container which maintains an atmosphere of low humidity through the use of a suitable drying agent which occupies the bottom part of the desiccator. It is used both for the cooling of heated objects and for the storage of dry objects that must not be exposed to the moisture normally present in the atmosphere.
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The desiccator you will be using is made of aluminum. The desiccant we will be using is anhydrous CaCl2. An airtight seal is maintained by applying silicone grease to the surfaces where the lid and body of the desiccator meet. Be careful not to add too much grease. Once the desiccant has been added, the lid to the desiccator should not be removed any more than is necessary.
An ignited crucible or other very hot object should be cooled for about one minute before being placed into the desiccator. In either case, the lid of the desiccator should be slightly ajar for 30 seconds prior to complete closing. This will prevent a partial vacuum from forming as the heated air cools. If such a vacuum forms it might become very difficult to remove the lid without upsetting the samples within.
A dried sample should remain in the desiccator for at least 5 minutes before being weighed. If the sample is to remain in the desiccator for an extended period of time before weighing, the top of the weighing bottle of the lid of the vial should be put in place after 10 minutes of cooling.
Several experiments will require some skill in using a desiccator. To open the desiccator, slide the lid gently as shown at left. If you feel or hear metal scraping against metal when you slide off the lid, then a small amount of silicon grease needs to be rubbed around the flat surface of the lid. Squeeze a VERY small amount of grease onto your finger, as at the right,
and rub it all around the flat surface of the lid.
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The desiccator contains a plate with holes over a screen which covers granulated anhydrous calcium sulfate, a desiccating or dehydrating agent. The desiccator ought not to be left open except to transfer samples in or out of it.