Drying tube
The drying tube is a straight, angled or U-shaped glass tube, at one end there is usually a standard ground joint , the second end is open. There are designs with and without a stopcock plug .
Filling
The drying tube is first filled with a little cotton wool, then with solid desiccants (e.g. calcium chloride or silica gel ) and the open end is then "closed" again with some cotton wool.
use
The drying tube is placed on vessels (e.g. round-bottom flasks) or apparatuses using the standard ground joint that contain moisture-sensitive or hygroscopic substances that are to be protected from air humidity .