Suitability of Individual Desiccants

Alumina. (Preheated to 175° for about 7h). Mainly as a drying agent in a desiccator or as a column through which liquid is percolated. 

Aluminium amalgam. Mainly used for removing traces of water from alcohols via refluxing followed by distillation. 

Barium oxide. Suitable for drying organic bases. 

Barium perchlorate. Expensive. Used in desiccators (covered with a metal guard). Unsuitable for drying solvents or organic material where contact is necessary, because of the danger of EXPLOSION 

Boric anhydride. (Prepared by melting boric acid in an air oven at a high temperature, cooling in a desiccator, and powdering.) Mainly used for drying formic acid. 

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When well-formed individual crystals have been obtained, filter them on a Witte plate, wash once with dilute nitric acid (1 3), pump as dry as possible, place the moist crystals in a suitable vessel, and put this in a desiccator over sulfuric acid. Watch the crystals carefully, with occasional stirring, and bottle them at once when they are dry. Do not touch them with the fingers, as this will discolor them. If they are allowed to overdry in the desiccator, they lose both crystal water and nitric acid and turn into a sticky mass of brownish-colored basic salt, which will not take up water from the air to reverse the reaction. Consequently, effloresced crystals cannot be used to complete the drying of the moist crystals. If the crystals are exposed to moist air, they deliquesce, undergo hydrolysis in the resulting solution, and form a basic salt. If they are bottled before they are dry, they will in time become discolored. If properly prepared, they will remain perfectly transparent and have a very pretty amethyst color, the intensity of which depends upon the size of the crystals. Crystals of iron alum have the same color. 

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