Glass tubes or glass tubing are hollow pieces of borosilicate or flint

Flint glass

Flint glass is optical glass that has relatively high refractive index and low Abbe number. Flint glasses are arbitrarily defined as having an Abbe number of 50 to 55 or less. The currently known flint glasses have refractive indices ranging between 1.45 and 2.00...

 glass used primarily as laboratory glassware

Laboratory glassware

Laboratory glassware refers to a variety of equipment, traditionally made of glass, used for scientific experiments and other work in science, especially in chemistry and biology laboratories...

. Glass tubing is commercially available in various thicknesses and lengths. Glass tubing is frequently attached to rubber stopper

Stopper (plug)

A bung is truncated cylindrical or conical closure to seal a container, such as a bottle, tube or barrel. Unlike a lid which encloses a container from the outside without displacing the inner volume, a bung is partially inserted inside the container to act as a seal...

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In the past, scientists constructed their own laboratory apparatus prior to the ubiquity of interchangeable 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...

s. Today, commercially available parts connected by ground glass joints are preferred; where specialized glassware are required, they are made to measure using commercially available glass tubes by specialist glassblowers. For example, 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...

 is made of two large glass tubes, connected by stopcocks and smaller glass tubes, which are further connected to plastic hoses.

Modifying

Although modifying glass tubing is no longer an essential laboratory technique, many are still familiar with the basic methods. A glass cutter

Glass cutter

A glass cutter is a hand tool used to make a shallow score in one side of the surface of flat glass that is to be broken in two pieces. The scoring encourages the glass to break along the score, and not in an undesired direction...

 is used to break pieces of glass tubing into smaller pieces. Freshly cut edges are flame polished

Flame polishing

Flame polishing is a method of polishing a material, usually thermoplastics or glass, by exposing it to a flame or heat. By melting the surface of the material, surface tension smooths the surface out. Operator skill is critical with this method. When done properly, flame plastic polishing produces...

 before use to remove the rough edge. Glass tubing can be bent by heating evenly over a Bunsen flame

Bunsen burner

A Bunsen burner, named after Robert Bunsen, is a common piece of laboratory equipment that produces a single open gas flame, which is used for heating, sterilization, and combustion.- Operation:...

 to red heat

Red heat

The practice of using colours to determine the temperature of a piece of ferrous metal comes from blacksmithing. Long before thermometers were widely available it was necessary to know what state the metal was in for heat treating it and the only way to do this was to heat it up to a colour which...

. Hose barb

Hose barb

Hose barbs are cylindrical pieces or parts for attaching and securing of hoses . The barb-like rings on the cylindrical piece allow for an easy push-connection of flexible-plastic or rubber tubing that is not so easily disconnected. Hose barbs are used in machine perfusion and chemistry laboratory...

s can be added to tubing, giving a better grip and seal for attaching plastic or rubber tubing.