Exsiccator

EXSICCATOR, an apparatus intended for preserving an object placed inside it without access to moisture from the air or for drying it; it consists of a thick-walled glass vessel of special shape with a carefully ground glass lid (Fig. 1). Substances that avidly absorb moisture are placed in the bottom of the exsiccator: dry calcium chloride, concentrated sulfuric acid, and sometimes phosphorus anhydride. A porcelain or metal insert with holes (Fig. 2) or a metal mesh circle is placed on the inner wall; the objects placed in the exsiccator for drying or protection from moisture are set on these inserts. For preserving substances that change under the influence of _O2 of air, and for the rapid drying of substances that decompose under the influence of heat or moisture, vacuum exsiccators are used, which have an opening with a stopcock in the wall or lid (Fig. 3). With the help of this stopcock, a pump is connected and the air is evacuated from the exsiccator; the decrease in pressure facilitates the evaporation of moisture, accelerates diffusion, and reduces the action of _O3

Figure 2.

Figure 3. (see Vacuum apparatus). There also exist vacuum exsiccators with an electric heater inside. Pregl proposed for elementary organic microanalysis a special micro-exsiccator. It is a tube divided in the middle by a capillary into two parts (Fig. 4). On one side, the substance to be dried is placed, and on the other side, calcium chloride is packed. By connecting the end of the micro-exsiccator where the substance is located to a vacuum pump, a vacuum is obtained in this part and at the same time a slow stream of dry air from the capillary, which promotes rapid drying of the substance. Exsiccators can also be adapted for absorbing vapors of other liquids. It is only necessary to place the appropriate substance in the bottom of the exsiccator: for example, for absorbing vapors of benzene, chloroform, petroleum ether, paraffin shavings can be used.