Drying tube
Encyclopedia
Desiccant
A desiccant is a hygroscopic substance that induces or sustains a state of dryness in its local vicinity in a moderately well-sealed container....
, wherein at one end the tube-like structure terminates in a ground glass joint
Ground glass joint
Ground glass joints are used in laboratories to quickly and easily fit leak-tight apparatus together from commonly available parts. For example, a round bottom flask, Liebig condenser, and oil bubbler with ground glass joints may be rapidly fitted together to reflux a reaction mixture...
for use in connecting the drying tube to a reaction vessel, for the purpose of keeping that reaction vessel free of moisture.
The tube-like structure is often bent and can also widen to form a bulb/desiccant reservoir. Typically a drying tube is 1–2 cm wide and 5–10 cm long and bent at an angle of about 90 degrees. In use, the drying tube is filled with a rechargeable desiccant
Desiccant
A desiccant is a hygroscopic substance that induces or sustains a state of dryness in its local vicinity in a moderately well-sealed container....
such as calcium chloride
Calcium chloride
Calcium chloride, CaCl2, is a salt of calcium and chlorine. It behaves as a typical ionic halide, and is solid at room temperature. Common applications include brine for refrigeration plants, ice and dust control on roads, and desiccation...
, and the open end of drying tube is partially blocked (e.g. with wool, glasswool or a bung/cork which has a small bore made in it) and the drying tube is connected to the apparatus to be kept dry via the ground glass joint. If the drying tube is bent the bend is oriented so that solid desiccant does not fall into the reaction vessel. Some drying tubes have a glass sinter to prevent desiccant falling into the reaction vessel. Drying tubes are often prepared in advance and the desiccant can be replaced when exhausted.
Reactions which are being heated, or which evolve gases, must never be sealed because an overpressure may shatter the vessel. Drying tubes are usually fitted on top of the reflux condenser
Condenser (laboratory)
In a laboratory a condenser is a piece of laboratory glassware used to cool hot vapors or liquids. A condenser usually consists of a large glass tube containing a smaller glass tube running its entire length, within which the hot fluids pass....
, allowing the pressure to be relieved while excluding atmospheric moisture.
Drying tubes are often used in less-demanding applications, typically in organic syntheses
Organic Syntheses
Organic Syntheses is a scientific journal that since 1921 has provided the chemistry community with annual collections of detailed and checked procedures for the organic synthesis of organic compounds. The journal is peer reviewed...
. One good example is the Fultz reaction. While the reaction is often carried out at room temperature, the solvent, usually volatile diethyl ether
Diethyl ether
Diethyl ether, also known as ethyl ether, simply ether, or ethoxyethane, is an organic compound in the ether class with the formula . It is a colorless, highly volatile flammable liquid with a characteristic odor...
or tetrahydrofuran
Tetrahydrofuran
Tetrahydrofuran is a colorless, water-miscible organic liquid with low viscosity at standard temperature and pressure. This heterocyclic compound has the chemical formula 4O. As one of the most polar ethers with a wide liquid range, it is a useful solvent. Its main use, however, is as a precursor...
is already able to displace air directly, making additional measures to exclude atmospheric moisture less important.
An oil bubbler
Oil bubbler
An gas bubbler is a piece of laboratory glassware which consists of a glass bulb filled with a small amount of fluid — usually mineral or silicone oil, less commonly mercury. The inlet to the bulb is connected to a ground glass joint, while the outlet is vented to the air.Gas bubblers are...
may be a useful substitute. In this case, gases are allowed to escape, but air is not able to enter because the bubbler acts as a one-way valve. Oil bubblers can tolerate an underpressure in the reaction vessel. Oil is sucked into a sump in lieu of air. However, if the pressure in the reaction vessel falls too low, the oil may be sucked into the reaction vessel, contaminating it.
For more demanding applications, a Schlenk line
Schlenk line
225px|thumb|Vacuum gas manifold set up: 1 inert gas in, 2 inert gas out , 3 vacuum 4 reaction line, 5 Teflon tap to gas, 6 Teflon tap to vacuum 225px|thumb| Vacuum gas manifold set up: 1 inert gas in, 2 inert gas out , 3 vacuum , 4 reaction line, 5 double oblique stopcock...
or glovebox
Glovebox
A glovebox is a sealed container that is designed to allow one to manipulate objects where a separate atmosphere is desired. Built into the sides of the glovebox are gloves arranged in such a way that the user can place their hands into the gloves and perform tasks inside the box without breaking...
may be used to provide an atmosphere of dry, inert gas
Inert gas
An inert gas is a non-reactive gas used during chemical synthesis, chemical analysis, or preservation of reactive materials. Inert gases are selected for specific settings for which they are functionally inert since the cost of the gas and the cost of purifying the gas are usually a consideration...
such as argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
or nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
.