Desiccating agents

Phosphorus(V) oxide is an extremely effective desiccating agent, reducing the vapour pressure of water over it to a negligibly small... 

Anhydrous magnesium sulphate. This is an excellent, neutral desiccating agent and is inexpensive. It is rapid in its action, chemically inert and fairly efficient, and can be employed for most compounds including those (esters, aldehydes, ketones, nitriles, amides, etc.) to which calcium chloride is not applicable. 

Desiccating agents used in corrosion prevention must be cheap, easy to handle and non-corrosive. These requirements rule out many of the familiar laboratory desiccants, and in practice the most common packaging desiccants are silica gel, activated alumina and quicklime (calcium oxide). Activated... 

Desiccating agents can be exposed on open trays in store rooms, but in some cases, continuous circulation of the air through the desiccant may be preferable. Finely divided desiccant should be prevented from reaching exposed metal surfaces. 

To prevent waste, the receiver should be followed by a flask containing methyl alcohol, and fitted with a calcium chloride tube. The apparatus should be placed in a hood behind a screen of thick plate-glass because anhydrous hydrazoic acid is very liable to explode violently at room temp. The hands should be protected by heavy gloves, and the face by a mask with plate-glass goggles. For phosphorus pentoxide as a desiccating agent, vide infra. 

The most difficult impurity to eliminate is hydrogen, which is nearly always formed simultaneously with the phosphine. G. Ter-Gazarian found the most effective method of purifying the gas from traces of other hydrogen phosphides, and from hydrogen is repeated liquefaction and fractional distillation of the liquid. F. M. G. Johnson recommended alumina, dehydrated at a low temp., as a desiccating agent for the gas. 

Anhydrous copper sulphate absorbs moisture strongly, and is also used as a desiccating agent, however it does not become wet. 

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