Setup for purification of solvent (here: tetrahydrofuran over sodium/benzophenone)
The standard setup consists of a 2 L round-bottomed flask that is charged with a solvent and the drying agent, a head, a reflux condenser (it can't be seen here because it is in the upper part of the fume hood) and a heating mantle. The heating mantle is connected to a Variac that controls the power output. When it comes to drying solvents, there are several things to consider:
1. The solvent purification setup has to be well maintained. The flask has to be clean in regular intervals. The remaining drying agent has to be quenched properly and disposed off. Solvent stills that have been operated for too long without maintainance pose a serious safety risk. Bases slowly dissolve the glass of round-bottomed flask! In addition, the remainder of the drying agent are difficult to deactivate if it is covered with a lot of byproducts.
2. One has to make sure to use the appropriate drying agent for the solvent. If one is not 100% sure, it is always better check before before causing an accident. It is not uncommon that choosing the wrong drying agent led to serious explosions and accidents. See also Drying solvents.