Two small test tubes held in spring clamps
|Other names||Culture tube|
A test tube, also known as a culture tube or sample tube, is a common piece of laboratory glassware consisting of a finger-like length of glass or clear plastic tubing, open at the top, usually with a rounded U-shaped bottom.
A large test tube designed specifically for boiling liquids is called a boiling tube.
Test tubes are available in a multitude of lengths and widths, typically from 10 to 20 mm wide and 50 to 200 mm long. The top often features a flared lip to aid pouring out the contents; some sources consider that the presence of a lip is what distinguishes a test tube from a culture tube. A test tube has either a flat bottom, a round bottom, or a conical bottom. Some test tubes are made to accept a ground glass stopper or a screw cap. They are often provided with a small ground glass or white glaze area near the top for labeling with a pencil.
Test tubes are widely used by chemists to hold, mix, or heat small quantities of solid or liquid chemicals, especially for qualitative experiments and assays. Their round bottom and straight sides minimize mass loss when pouring, make them easier to clean, and allow convenient monitoring of the contents. The long, narrow neck slows down the spreading of vapors and gases to the environment.
Culture tubes are often used in biology for handling and culturing all kinds of live organisms, such as molds, bacteria, seedlings, plant cuttings, etc.; and in medicine and forensics to store samples of blood or other fluids.
A test tube with a stopper is often used for temporary storage of chemical or biological samples.
Test tubes are usually held in special-purpose racks, clamps, or tongs. Some racks for culture tubes are designed to hold the tubes in a nearly horizontal position, so as to maximize the surface of the culture medium inside.
Test tubes for physics and chemistry are usually made of glass for better resistance to heat and corrosive chemicals and longer life. Tubes made from expansion-resistant glasses, such as borosilicate glass, can be placed directly over a Bunsen burner flame.
Test tubes may come with prepared contents. For example, a blue top tube is a test tube of 5 ml containing sodium citrate as an anticoagulant, used to collect specimens for coagulation screens and testing for glucose-6-phosphate dehydrogenase.
See also 
- MiniScience.com catalog: Test Tube, accessed March 27, 2009
- Thomas Scott (transl., 1996), Concise Encyclopedia: Biology. Walter de Gruyter. ISBN 3-11-010661-2, ISBN 978-3-11-010661-9. 1287 pages.
- M. Jeremy Ashcraft, General Manager, Lake Charles Manufacturing (2007). Test Tube Molding Process: A discussion on the molding of plastic test tubes. Lake Charles Manufacturing.
- TheFreeDictionary > blue top tube Citing: McGraw-Hill Concise Dictionary of Modern Medicine. 2002 by The McGraw-Hill Companies, Inc.
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