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A test tube, also known as a culture tube or sample tube, is a common piece of
laboratory glassware Laboratory glassware is a variety of equipment used in science, scientific work, traditionally made of glass. Glass may be blown, bent, cut, molded, or formed into many sizes and shapes. It is commonly used in chemistry, biology, and analytical ...
consisting of a finger-like length of
glass Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...
or clear
plastic Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...
tubing, open at the top and closed at the bottom. Test tubes are usually placed in special-purpose
rack Rack or racks may refer to: Storage, support and transportation * Amp rack, a piece of furniture in which amplifiers are mounted * Autorack or auto carrier, for transporting vehicles in freight trains * Baker's rack, for bread and other bake ...
s.


Types and usage


Chemistry

Test tubes intended for general chemical work are usually made of glass, for its relative resistance to heat. Tubes made from expansion-resistant glasses, mostly
borosilicate glass Borosilicate glass is a type of glass with silica and boron trioxide as the main glass-forming constituents. Borosilicate glasses are known for having very low coefficients of thermal expansion (≈3 × 10−6 K−1 at 20 °C), ma ...
or
fused quartz Fused quartz, fused silica or quartz glass is a glass consisting of almost pure silica (silicon dioxide, SiO2) in amorphous (non-crystalline) form. This differs from all other commercial glasses, such as soda-lime glass, lead glass, or borosi ...
, can withstand high temperatures up to several hundred degrees
Celsius The degree Celsius is the unit of temperature on the Celsius temperature scale "Celsius temperature scale, also called centigrade temperature scale, scale based on 0 ° for the melting point of water and 100 ° for the boiling point ...
. Chemistry 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. A chemistry test tube typically has a flat bottom, a round bottom, or a conical bottom. Some test tubes are made to accept a
ground glass stopper Ground glass joints are used in laboratories to quickly and easily fit leak-tight apparatus together from interchangeable commonly available parts. For example, a round bottom flask, Liebig condenser, and oil bubbler with ground glass joints ma ...
or a
screw cap A screw cap or closure is a common type of closure for bottles, jars, and tubes. History Screw caps had been used in Europe since the 1500s and a British patent was filed in 1810 by Peter Durand acting on behalf of Nicolas Appert. John Lan ...
. They are often provided with a small
ground glass Ground glass is glass whose surface has been ground to produce a flat but rough ( matte) finish, in which the glass is in small sharp fragments. Ground glass surfaces have many applications, ranging from ornamentation on windows and table glass ...
or white glaze area near the top for labelling with a pencil. Test tubes are widely used by
chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a graduated scientist trained in the study of chemistry, or an officially enrolled student in the field. Chemists study the composition of ...
s to handle chemicals, especially for qualitative experiments and assays. Their spherical bottom and vertical sides reduce mass loss when pouring, make them easier to wash out, and allow convenient monitoring of the contents. The long, narrow neck of test tube slows down the spreading of gases to the environment. Test tubes are convenient containers for heating small amounts of liquids or solids with a
Bunsen burner A Bunsen burner, named after Robert Bunsen, is a kind of ambient air gas burner used as laboratory equipment; it produces a single open gas flame, and is used for heating, sterilization, and combustion. The gas can be natural gas (which is main ...
or
alcohol burner An alcohol burner or spirit lamp is a piece of laboratory equipment used to produce an open flame. It can be made from brass, glass, stainless steel or aluminium. Uses Alcohol burners are preferred for some uses over Bunsen burners for safety pu ...
. The tube is usually held by its neck with a clamp or
tongs Tongs are a type of tool used to grip and lift objects instead of holding them directly with hands. There are many forms of tongs adapted to their specific use. Design variations include resting points so that the working end of the tongs d ...
. By tilting the tube, the bottom can be heated to hundreds of degrees in the flame, while the neck remains relatively cool, possibly allowing vapours to condense on its walls. A
boiling 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 and closed at the bottom. Test tubes are usually placed in s ...
is a large test tube intended specifically for boiling liquids. A test tube filled with water and upturned into a water-filled beaker is often used to capture
gas Gas is a state of matter that has neither a fixed volume nor a fixed shape and is a compressible fluid. A ''pure gas'' is made up of individual atoms (e.g. a noble gas like neon) or molecules of either a single type of atom ( elements such as ...
es, e.g. in
electrolysis In chemistry and manufacturing, electrolysis is a technique that uses Direct current, direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of c ...
demonstrations. A test tube with a stopper is often used for temporary storage of chemical or biological samples.


Biosciences

Culture tubes are test tubes used in
biology Biology is the scientific study of life and living organisms. It is a broad natural science that encompasses a wide range of fields and unifying principles that explain the structure, function, growth, History of life, origin, evolution, and ...
and related sciences for handling and culturing all kinds of live
organisms An organism is any living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have been pr ...
, such as molds,
bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...
, seedlings, cutting (plant), plant cuttings, etc.. 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. Culture tubes for biology are usually made of clear plastic (such as polystyrene or polypropylene) by injection molding and are often discarded after use. Plastic test tubes with a screwtop cap are often called "Falcon tubes" after a line manufactured by Becton Dickinson. Some sources consider that the presence of a lip is what distinguishes a test tube from a culture tube.


Clinical medicine

In clinical medicine, sterile test tubes with air removed, called vacutainers, are used to collect and hold biological specimen, samples of physiological fluids such as blood, urine, pus, and synovial fluid. These tubes are commonly sealed with a rubber stopper and often have a specific additive placed in the tube with the stopper color indicating the additive. For example, a ''blue-top tube'' is a 5 milliliter, ml test tube containing Trisodium citrate, sodium citrate as an anticoagulant, used to collect blood for coagulation screen, coagulation and glucose-6-phosphate dehydrogenase testing. Small vials used in medicine may have a snap-top (also called a hinge cap) molded as part of the vial.


Other uses

Test tubes are sometimes put to casual uses outside of lab environments, e.g. as flower vases, glassware for certain weak shooter (mixed drink), shots, or containers for spices. They can also be used for raising queen ants during their first months of development.


Variants


Boiling tube

A boiling tube is a small cylindrical vessel used to strongly heat substances in the flame of a
Bunsen burner A Bunsen burner, named after Robert Bunsen, is a kind of ambient air gas burner used as laboratory equipment; it produces a single open gas flame, and is used for heating, sterilization, and combustion. The gas can be natural gas (which is main ...
. A boiling tube is essentially a scaled-up test tube, being about 50% larger. They are designed to be wide enough to allow substances to boil violently as opposed to a test tube, which is too narrow; a boiling liquid can explode out of the end of test tubes when they are heated, as there is no room for bubbles of gas to escape independently of the surrounding liquid. This phenomenon is called Bumping (chemistry), bumping.


Ignition tube

An ignition tube is used in much the same way as a boiling tube, except it is not as large and thick-walled. It is primarily used to hold small quantities of substances which are undergoing direct heating by a Bunsen burner or other heat source. This type of tube is used in the sodium fusion test. Ignition tubes are often difficult to clean due to the small bore. When used to heat substances strongly, some Char (chemistry), char may stick to the walls as well. They are usually disposable.


See also

* Test tube holder * Test tube brush * Microtiter plate


References

{{Laboratory equipment Laboratory glassware Containers