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. Some of the equipment is
now made of plastic for cost, ruggedness, and convenience reasons, but
glass is still used for some applications because it is relatively inert,
transparent, more heat-resistant than some plastic up to a point, and
relatively easy to customize. Borosilicate glasses—formerly called
Pyrex—are often used because they are less subject to thermal stress. For
some applications quartz is used for its ability to withstand high
temperatures or its transparency in certain parts of the electromagnetic
spectrum. In some applications, especially some storage bottles, darkened
brown glass is used to keep out much of the outside light so that the
effect of light on the contents inside is minimized. Special-purpose
materials are also used; for example, hydrofluoric acid is stored and used
in polyethylene containers because it attacks glass.
There are many different kinds of laboratory glassware items, the majority
of which are covered in separate articles of their own; see the list
further below. Such glassware is used for a wide variety of functions
which include volumetric measuring, holding or storing chemicals or
samples, mixing or preparing solutions or other mixtures, containing lab
processes like chemical reactions, heating, cooling, distillation,
separations including chromatography, synthesis, growing biological
organisms, spectrophotometery, and containing a full or partial vacuum.
When in use, laboratory glassware is often held in place with clamps made
for that purpose, which are likewise attached and held in place by stands
or racks. This article covers aspects of laboratory glassware which may be
common to several kinds of glassware and may briefly describe a few
glassware items not covered in other articles.
Ground glass joints
In a lab experiment or process—such as a distillation or a reflux—ground
glass joints make it possible to rapidly assemble the set-up from
component glassware items in a leak-tight but non-permanent way. Using old
technology, this was often done with rubber (or possibly cork) stoppers
inserted between the component glassware items. Holes could be made in
such stoppers to insert glass tubes or the ends of some glass items.
However, rubber (and of course cork) are not as chemically inert or
heat-resistant as glass and degrade with age. In order to connect the
hollow inner spaces of the glassware components, these types of joints are
hollow on the inside and open at the ends, except for stoppers.
Two general types of ground glass joints are fairly commonly used: joints
that are slightly conically-tapered and ball and socket joints (sometimes
called spherical joints).
Conically tapered joints
Conically tapered ground glass joints consist of a male and a female half
which are manufactured to a standard 1:10 taper. Apart from stoppers, most
conically tapered joints are hollow to allow liquids or gases to flow
through. An example of the use of conically-tapered joints is to join a
round bottom flask, Liebig condenser, and oil bubbler together to allow a
reaction mixture to be refluxed.
Conically tapered ground glass joints. Inner (male) joint shown on the
left and outer (female) joint shown on the right. Ground glass surfaces
are shown with gray shading. By putting them together in the direction of
the arrows, they can be joined, usually with some grease applied to the
ground glass surfaces.
Here, the inner joint is a ball and the outer joint is a socket, both
having holes leading to the interior of their respective tube ends to
which they are fused. Ball and socket joints are used where some degree of
free-play is necessary, such as when joining a cold trap to a gas manifold
for a Schlenk line.
Ground glass ball (left) and socket (right) joints. The ground glass
surfaces are shown with gray shading. By putting them together in the
direction of the arrows, they can be joined, with some grease applied to
the ground glass surfaces.
For either standard taper joints or ball-and-socket joints, inner and
outer joints with the same numbers are made to fit together. When the
joint sizes are different, ground glass adapters may be available (or
made) to place in between to connect them. Special clips or pinch clamps,
known as Keck clips, may be placed around the union of the joints to help
keep them together.
Grease is used to lubricate glass stopcocks and joints. Some laboratories
fill them into syringes for easy application. Two typical examples: Left -
Krytox, a fluoroether-based grease; Right - a silicone-based high vacuum
grease by Dow Corning.
Lubrication and sealing
A thin layer of grease is usually applied to the ground-glass surfaces to
be connected, and the inner joint is inserted into the outer joint such
that the ground-glass surfaces of each are next to each other to make the
connection. The use of grease helps to provide a good seal and prevents
the joint from seizing, allowing the parts to be disassembled easily.
PTFE (Teflon) sleeves and PTFE sealing rings have been used in between
joints to fit them together instead of grease.
Laboratory glassware, such as Buchner flasks and Liebig condensers, may
have tubular glass tips serving as hose connectors with several ridged
hose barbs around the diameter near the tip. This is so that the tips can
have the end of a rubber or plastic tube mounted over them to connect the
glassware to another system such as a vacuum, water supply, or drain. A
special clip may be placed over the end of the flexible tube surrounding
the connector tip to prevent the hose from slipping off the connector.
Stopcocks are basically valves. They are often parts of laboratory
glassware such as burettes, separatory funnels, and columns used for
column chromatography. The stationary outer body of the stopcock is
typically made of glass, since it is fused with the rest of the glass
item. The inner plug or rotor, which can be rotated inside the body to
control flow through the stopcock, has one (or more) holes going through
it which serve as a fluid pathway(s).
The inner plug or rotor can be made of plastic (usually PTFE) or glass.
When it is plastic, the stopcock body's inner glass surface contacting it
is typically smooth glass. When it is made of glass, the contacting glass
surfaces are typically both ground-glass surfaces with stopcock grease
used between them for lubrication. High vacuum glass manifolds typically
use specially fitted, non-interchangeable all-glass stopcocks. Such
stopcocks are often available separately with some lengths of glass tubing
at the ports so that glass blowers can use them to make custom glass
manifolds for vacuum lines.
Rotaflo is a brand of specialty stopcocks. They generally consist of a
threaded PTFE plug which fits a correspondingly threaded glass barrel. By
screwing down the barrel, the flow can be stopped completely.
PTFE stopcocks usually wear out fairly quickly. On the other hand, they
are interchangeable, making replacements easy, compared with fitted glass
There are also glass joints available sometimes which use an O-ring
between them to form a leak-tight seal. Such joints are more
symmetrical in theory with a tubular joint on each side having a widened
tip with a concentric circular groove into which an elastomer O-ring can
be inserted between the two joints. O-ring joints are sized based on the
inner diameter in mm of the joint. Since they can come apart rather
easily, a clip or pinch clamp is needed to hold them together. The
elastomer of the O-ring is more limited in high temperature resistance
than other types of glass joints using high temperature grease.
Glass O-ring joints with elastomer O-ring in between. By putting them
together in the direction of the arrows with an appropriately-sized O-ring
placed in between in circular grooves on each joint (not shown on the
joint on the left side for simplicity), they can be joined.
Round slightly spiral threaded connections are possible on tubular ends of
glass items. Such glass threading can face the inside or the outside. In
use, glass threading is screwed into or onto non-glass threaded material
such as plastic. Glass vials typically have outer threaded glass openings
onto which caps can be screwed on. Bottles and jars in which chemicals are
sold, transported, and stored usually have threaded openings facing the
outside and matching non-glass caps or lids.
Glass-to-metal transition joints
Occasionally, it may be desired to fuse a glassware item to a metal item
with a tubular pathway between them. This requires the use of a
glass-to-metal transition joint. Most glass used in laboratory glassware
does not have the same coefficient of thermal expansion as metal, so
fusing the usual type of glass with metal is likely to result in cracking
of the glass. These special transition joints have several short sections
of special types of glass fused together between the metal and the usual
type of glass, each having more gradual changes in thermal expansion
Fritted glass is finely porous glass through which gas or liquid may pass.
It is made by sintering together glass particles into a solid but porous
body.This porous glass body can be called a frit. Applications in
laboratory glassware include use in fritted glass filter items, scrubbers,
or spargers. Other laboratory applications of fritted glass include
packing in chromatography columns and resin beds for special chemical
In a fritted glass filter, a disc or pane of fritted glass is used to
filter out solid particles, precipitate, or residue from a fluid, similar
to a piece of filter paper. The fluid can go through the pores in the
fritted glass, but the frit will often stop a solid from going through. A
fritted filter is often part of a glassware item, so fritted glass funnels
and fritted glass crucibles are available.
Laboratory scale spargers, scrubbers, and gas-washing bottles are similar
glassware items which may use a fritted glass piece fused to the tip of a
gas-inlet tube. This fritted glass tip is placed inside the vessel with
liquid inside during use such that the fritted tip is submerged in the
liquid. To maximize surface area contact of the gas to the liquid, a gas
stream is slowly blown into the vessel through the fritted glass tip so
that it breaks up the gas into many tiny bubbles. The purpose of sparging
is to saturate the enclosed liquid with the gas, often to displace another
gaseous component. The purpose of a scrubber or gas-washing bottle is to
scrub the gas such that the liquid absorbs one (or more) of the gaseous
components to remove it from the gas stream, effectively purifying the gas
Cleaning laboratory glassware
There are many different methods of cleaning laboratory glassware. Most of
the time, these methods  are tried in this order:
The glassware is soaked in a detergent solution to remove grease and
loosen most contamination
Gross contamination and large particles are removed mechanically, by
scrubbing with a brush or scouring pad.
Alternatively, the first two steps may be combined by sonicating the
glassware in a hot detergent solution
Solvents known to dissolve the contamination are used to rinse the
glassware and remove the last traces
If the glassware are still dirty, more caustic methods may be needed. This
includes soaking the piece in a saturated solution of sodium or potassium
hydroxide in an alcohol ("base bath"), followed by a dilute solution of
hydrochloric acid ("acid bath") to neutralize the excess base. Sodium
hydroxide cleans glass by dissolving a tiny layer of silica, to give
Older methods involving aqua regia (for removing metals from frits),
piranha solution and chromic acid (for removing organics) are generally
considered unsafe because of possible explosions and the corrosive/toxic