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 such as 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. Special-purpose materials are also used; for example, hydrofluoric acid is stored and used in containers made of wax or polymer because it attacks glass.
Use of lab glassware
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 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, spectrophotometry, and containing a full or partial vacuum. 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.
Production of lab glassware
Most laboratory glassware is now mass-produced, but most large laboratories employ a glass blower to construct specialized pieces. This construction forms a specialized field of glassblowing requiring precise control of shape and dimension. In addition to repairing expensive or difficult to replace glassware, scientific glassblowing commonly involves fusing together various glass parts such as glass joints and tubing, stopcocks, transition pieces, and/or other glassware or parts of them to form items of glassware such as vacuum manifolds, special reaction flasks, etc.
Glass parts for making lab glassware
Various types of joints and stopcocks are available separately and come fused with a length of glass tubing which a glassblower may use to fuse to another piece of glassware.
Ground glass joints
In a lab experiment or process such as a distillation or a reflux, it is often desirable to 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. For this reason, many glassware items are now made with convenient ground glass joints for connecting the items together. 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.
Crude versions of conically-tapered ground glass joints have been made for quite a while, particularly for stoppers for glass bottles and retorts. These days, ground glass joints can be precisely ground to a reproducible taper or shape. They are made to join two glassware pieces together. One of the glassware items to be joined would have an inner (or male) joint with the ground glass surface facing outward and the other would have an outer (or female) joint of a correspondingly-fitting taper with the ground glass surface facing inward. A rather thin layer of grease particularly made for this application can be 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. In addition to making a leak-tight connection, the grease allows to joints to be later separated more easily.
Two general types of ground glass joints are fairly commonly used: joints which are slightly conically-tapered and ball and socket joints(sometimes called spherical joints).
Standard Taper symbol
- The conically-tapered ground glass joints typically have a 1:10 taper and are often labeled with a symbol consisting of a capital T overlaid on a capital S which stands for "Standard Taper". This symbol is followed by a number, a slash, and another number. The first number represents the outer diameter in millimeters (mm) at the base of an inner joint or the inner diameter in mm at the tip of an outer joint, in both cases where the applicable diameter is at a maximum in the joint. The second number represents the ground glass length of the joint in mm. These joint sizes apply only to glassware in the US. There are also European ISO standard joints. The stopper joints of chemical bottles, volumetric flasks, and separatory funnels often do not use the precision standard taper ground glass joints. Stopper joints are designated (if at all) only by the maximum diameter number. Fairly recently, Teflon sleeves have been used in between joints to fit them together instead of grease.
- For ball and socket joints, 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. The ball tip is a hemisphere with a ground glass surface on the outside which fits inside of the socket where the ground glass surface is on the inside. Ball and socket joints are labeled with a size code consisting of a number, a slash, and another number. The first number represents the outer diameter in mm of the ball at its base or the inner diameter in mm at the tip of a socket, in both cases where the diameters are their maximum in the joints. The second number represents the inner diameter of the hole in the middle of the ball or socket, which leads to the inner diameter of the tube fused to the joint.
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 may be placed around the union of the joints to help keep them together.
Round-bottom flasks often have one or more conically-tapered ground glass joint openings or necks. Conventionally, these joints at the flask necks are outer joints. Other adapters such as distillation heads and vacuum adapters are made with joints that fit in with this convention. If a flask or other container has an extra outer ground glass joint on it which needs to be closed off for an experiment, there are often conically-tapered inner ground glass stoppers available for such a purpose. In some cases, small hook-like protrusions made of glass may be fused onto the rest of the glass item near a joint to allow an end loop of a small spring to be attached so the spring helps keep joints temporarily together. The use of a special very small size of conically-tapered fitting for glass, plastic, or metal parts called a Luer fitting or adapter has become more widespread. Originally, Luer fittings were mostly used to connect the hub of a needle to a syringe. Where the use of ground glass presents a problem such as in the production or distillation of diazomethane, which may explode on contact with rougher surfaces, equipment with smooth glass joints may be used.
Hose connections
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
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). This inner plug or rotor can be made of plastic 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 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.
O-ring joints
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.
Threaded connections
Round slightly spiral threaded connections such as those on the mouths of glass jars 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 threaded glass openings onto which caps can be screwed on.
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 coefficients.
Fritted glass
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 synthesis.
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. A gas stream is rather slowly blown into the vessel through the fritted glass tip so that it breaks up the gas entering the liquid into many tiny bubbles in order to maximize surface area contact of the gas to the liquid. 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 stream.
List of laboratory glassware
Laboratory glassware includes:
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- glass parts for lab glassware
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- stopcocks (essentially valves)
- ground glass joints, including conically tapered and ball and socket
- glass tubing in general and specifically capillary tubing
- glass stoppers
- glass-to-metal transition pieces
- fritted glass pieces
External links
The content of this page is retrieved from http://en.wikipedia.org/wiki/Laboratory_glassware under GFDL
