A test tube, also known as a culture tube or sample tube, is a common piece of laboratory equipment consisting of a finger-like length of clear plastic tubing, open at the top, usually with a rounded U-shaped bottom.
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 vapours and gases to the environment.
A test tube filled with water and upturned into a water-filled beaker is often used to capture gases, e.g. in electrolysis demonstrations.
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.
Where large numbers of tests are run or only small amounts are available for testing, or both, microtiter plates are often used as small test tubes.
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