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Laboratory glassware
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Three beakers, an Erlenmeyer flask, a graduated cylinder and a volumetric flask
Brown glass jars with some clear lab glassware in the background
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 plastics up to a point, and relatively easy to customize. Borosilicate glasses are often used because they are less subject to thermal stress and are common for reagent bottles. For some applications quartz glass is used for its ability to withstand high temperatures or its transparency in certain parts of the electromagnetic spectrum. In other applications, especially some storage bottles, darkened brown or amber (actinic) glass is used to keep out much of the UV and IR radiation so that the effect of light on the contents is minimized. Special-purpose materials are also used; for example, hydrofluoric acid is stored and used in polyethylene containers because it reacts with glass.[1] For pressurized reaction, heavy-wall glass is used for pressure reactor.
Contents
1 Applications
2 Production
3 Service temperatures
4 Keck clips
o 4.1 Safety when using vacuums
5 Gentle & even heating - baths & alternatives
6 Glassware joints
7 Glassware valves
o 7.1 Stopcock valve
o 7.2 Threaded plug valve
8 Fritted glass
9 Hermetic sealing
10 Cleaning laboratory glassware
11 Gallery
12 Notes
Applications
There are many different kinds of laboratory glassware items, the majority 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, spectrophotometry, and containing a full or partial vacuum, and pressure, like pressure reactor. 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. Production
Most laboratory glassware is now mass-produced, but many 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.
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. Service temperatures
Borosilicate glass, which makes up the majority of lab glass, may fracture if rapidly heated or cooled through a 150 °C (302 °F) temperature gradient. This is particularly true of large volume flasks, that can take hours to safely warm up. Gentle thermal cycling should be used when working with volumes more than hundreds of mLs to two liters. Whenever working with borosilicate glass, it is advisable to avoid sharp transitions between temperatures when the heating and cooling elements have a high thermal inertia. Glassware can be wrapped with tinfoil or insulated with wool to smooth out temperature gradients.
500 °C (932 °F) is the maximum service temperature for borosilicate glass as, at 510 °C (950 °F), thermal strain begins to appear in the structures. Operation at this temperature should be avoided and only intermittent. Bear in mind that glassware under vacuum will also have around one atmosphere of pressure on its surface before heating and so will be more likely to fracture as temperature transitions increase. Vacuum operation should be used if the atmospheric temperatures required are above a few hundred degrees Celsius, as this often has a dramatic effect on boiling points; significantly lowering them.
Borosilicate anneals at 560 °C (1,040 °F), this removes built in strain in the glass.
At 820 °C (1,510 °F), borosilicate glass softens and is likely to deform.[citation needed] And at 1,215 °C (2,219 °F) it becomes workable.
Quartz glass is far more resilient to thermal shock and can be operated continuously at 1,000 °C (1,830 °F). Thermal strain appears at 1,120 °C (2,050 °F), annealing occurs at 1,215 °C (2,219 °F) and it becomes workable at 1,685 °C (3,065 °F).
It is common for students and those new to working with glassware to set hotplates to a high value initially to rapidly warm a solution or solid. This is not only bad practice, as it can scorch the contents, it will almost universally burst large flasks, and this is one of the reasons why large flasks are often heated in water, oil, sand and steam baths or using a mantle that surrounds most, or all, of the flask. Keck clips
Keck clips and other clamping methods can be used to hold glassware together.
Safety when using vacuums
An absolute vacuum produces a pressure difference of one atmosphere, approximately 14 psi, over the surface of the glass. The energy contained within an implosion is defined by the pressure difference and the volume evacuated. Flask volumes can change by orders of magnitude between experiments. Whenever working with liter sized or larger flasks, chemists should consider using a safety screen or the sash of a flow hood to protect them from shards of glass, should an implosion occur. Glassware can also be wrapped with spirals of tape to catch shards, or wrapped with webbed mesh more commonly seen on scuba cylinders.
Glass under vacuum becomes more sensitive to chips and scratches in its surface, as these form strain accumulation points, so older glass is best avoided if possible. Impacts to the glass and thermally induced stresses are also concerns under vacuum. Round bottom flasks more effectively spread the stress across their surfaces, and are therefore safer when working under vacuum.
When connecting glassware, it is often tempting to use Keck clips on every joint, but this can be dangerous if the system is sealed or the exhaust is in any way restricted; e.g. by wash flasks or drying media. Many reactions and forms of operation can produce sudden, unexpected surges of pressure inside the glass. If the system is sealed or restricted, this can blow the glass apart. It is safer to only clip the joints that need holding together to stop them falling apart and to purposefully leave one or more unclipped; preferably those that are connected to lightweight, small objects like stoppers, thermometers or wash heads, that are pointing vertically upwards and not connected to other items of glassware. By doing so, any significant surge of pressure will cause these specifically chosen tapers to open and vent. This may seem counterintuitive, but it is safer and easier to deal with a controlled escape as opposed to the entire volume being uncontrollably released in an explosion. Gentle & even heating - baths & alternatives
This is a prerequisite for a lot of laboratory work as it protects the work itself and decreases the possibility of thermal strain fracturing the glass; see service temperatures for more information on this.
A common method is to fill a bowl surrounding the flask with water, oil, sand or steam, or to use a wrap around heating mantle.
However, baths can be extremely dangerous if they spill, overheat or ignite, they have a high thermal inertia (and so take a long time to cool down) and mantles can be very expensive and are designed for specific flask volumes. There are two alternative methods that can be used instead, where appropriate. When a heat source's minimum temperature is high, the glassware can be suspended slightly above the surface of the plate. This will not only reduce the ultimate temperature on the glass, it will slow down the rate of heat exchange and encourage more even heating; as there is no longer direct contact via a few points with the plate. Doing so works well for low boiling point operations.
If the glassware must be run at higher temperatures, a teepee setup can be used; so named as it looks a little like a tipi. This is when the glassware is suspended above the plate, but the flask is surrounded by a skirt of tinfoil. The skirt should start at the neck of the flask and drape down to the surface of the plate, not touching the sides of the flask. Having the base of the skirt cover the majority of the plates surface will effect better heat transfer. The flask will now be warmed indirectly by the hot air collecting under the skirt but, unlike simply suspending the glassware, it can now reach hundreds of degrees Celsius and is better protected from drafts.
Both these methods are useful as they are either cheaper or free, effective, safe and feature low thermal inertia transfer methods, meaning the chemist does not have to wait for a bath to cool down after use.
Baths are most useful when the heat source has little or no control over it. With the advent of variable temperature hotplates and wrap around mantles, their necessity has somewhat declined. The same can be said for many round bottom flask operations, which require the use of a bath. Glassware joints
Main article: 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. This is a large improvement compared with older methods of custom-made glassware, which was time-consuming and expensive, or the use of less chemical resistant and heat resistant corks or rubber bungs and glass tubes as joints, which took time to prepare as well.
To connect the hollow inner spaces of the glassware components, ground glass joints are hollow on the inside and open at the ends, except for stoppers. Glassware valves A very common straight bore glass stopcock attached with a plastic plug retainer. This stopcock is in the side arm of a Schlenk flask.
Describing glassware can be complicated since manufactures provide conflicting names for glassware. For example ChemGlass calls a glass stopcock what Kontes calls a glass plug. Despite this it is clear there are two main types of valves used in laboratory glassware, the stopcock valve and the threaded plug valve. These and other terms used below are defined in detail since they are bound to conflict with different sources.
Stopcock valve
Stopcocks are often parts of laboratory glassware such as burettes, separatory funnels, Schlenk flasks, and columns used for column chromatography. The stopcock is a smooth tampered plug or rotor with a handle, which fits into a corresponding ground glass female joint. The stationary female joint is designed such that it joins two or more pieces of glass tubing. The stopcock has holes bored through it which allow the tubes attached to the female joint to be connected or separated with partial turns of the stopcock. Most stopcocks are solid pieces with linear bores although some are hollow with holes to simple holes that can line up the joints tubing. The stopcock is held together with the female joint with a metal spring, plastic plug retainer, a washer and nut system, or in some cases vacuum. Stopcocks plugs are generally made out of ground glass or an inert plastic like PTFE. The ground glass stopcocks are greased to create an airtight seal and prevent the glass from fusing. The plastic stopcocks are at most lightly oiled.
Stopcocks are generally available individually with some length of glass tubing at the ports so that they can be joined by a glass blower into custom apparatus at the point of use. This is especially common for the large glass manifolds used in high vacuum lines.
More examples are featured in the gallery. This is a small sampling of stopcock valves; many additional variations exist in both plug boring and joint assembly.
Threaded plug valve A standard solid threaded plug valve with a double O-ring upper seal and PTFE to glass seal at its base
Threaded plug valves are used significantly in air-sensitive chemistry as well as when a vessel must be closed completely as in the case of Schlenk bombs. The construction of a threaded plug valve involves a plug with a threaded cap which are made so that they fit with the threading on a corresponding piece of female glass. Screwing the plug in part-way first engages one or more O-rings, made of rubber or plastic, near the plug's base, which seals the female joint off from the outer atmosphere. Screwing the plug valve all the way in engages the plug's tip with a beveled constriction in the glass, which provides a second seal. This seal separates the region beyond the bevel and the O-rings already mentioned.
With solid plugs, a tube or area exists above and below the bevel and turning the plug controls access. In a number of cases it is convenient to fully remove a plug which can give access to the region beyond the bevel. Plugs are generally made of an inert plastic such as PTFE and are attached to a threaded sleeve in such a way that the sleeve can be turned without spinning the plug. The contact with the bevel is made by an O-ring fitted to the tip of the plug or by the plug itself. There are a few examples where the plug in made of glass. In the case of glass plugs, the joint contact is always a rubber O-ring but they are still prone to shattering.
A thread T-bore plug valve used as a side arm on a Schlenk flask. Not all plugs are solid. Some plugs are bored with a T-junction. In these systems the plug extends beyond the threaded sleeve and is designed to form an airtight fitting with glass tubing or hosing. The shaft of the plug is bored from beyond the threaded sleeve to a T- junction just before the bevel plug contact. When the plug is fully sealed, the region beyond the bevel is separated from the plug shaft as well as the bore which leads out of its shaft. When the plug bevel contact is released, the two regions are exposed to each other. These valves have also been used as a grease-free alternative to straight bored stopcocks common to Schlenk flasks. The high symmetry and concise design of these valves has also made them popular for capping NMR tubes. Such NMR tubes can be heated without the loss of solvent thanks to the valve's gas-tight seal. NMR tubes with T-bore plugs are widely known as J. Young NMR tubes, named after the brand name of valves most commonly used for this purpose. Images of J. Young NMR tubes and a J. Young NMR tube adapter are in the gallery. Fritted glass
A Büchner funnel with a sintered glass disc
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.[2] 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.[3] Gas-washing bottle
Laboratory scale spargers (also known as gas diffusing stones or diffusors) as well as scrubbers, and gas-washing bottles (or Drechsel bottles[4]) 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 stream.
As frits are made up of particles of glass that are bonded together by small contact areas, it is wise to avoid using them in strongly alkaline conditions, as these can dissolve the glass to some extent. This is not normally a problem, as the amount dissolved is usually minute, but the equally minute bonds in a frit can be rotted away, causing the frit to fall apart over time. As such, consideration should be given to using frits in such solutions and they should be rapidly and thoroughly rinsed when cleaning the glass with bases like KOH. Hermetic sealing
Main article: Hermetic sealing
A thin layer of PTFE material or 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 this helps to provide a good seal and prevents the joint from seizing, allowing the parts to be disassembled easily.
Sealing allows chemists to easily see when a taper is leaking, as bubbles can usually be seen flowing through the taper. PTFE tape, bands, and fluoroether-based grease or oils, but not silicone-based, all emit hydrogen fluoride fumes as they approach and exceed their working temperature limits, which can occur when using a hotplate, mantle, oil bath or flame. Upon contact with moisture, including tissue, hydrogen fluoride immediately converts to hydrofluoric acid, which is highly corrosive and toxic, and requires immediate medical attention upon exposure. Cleaning laboratory glassware
There are many different methods of cleaning laboratory glassware. Most of the time, these methods[5][6] 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.
o 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
Acetone is often used for a final rinse of sensitive or urgently needed glassware as the solvent is miscible with water, and helps dilute and wash away remaining water from the glassware.
Glassware is often dried by suspending it upside down to drip dry on racks; these can include a hot air fan to blow the internals dry. Another alternative is to place the glassware under vacuum, lower the boiling points of the remaining volatiles.
If the glassware are still dirty, more drastic methods may be needed. This includes soaking the piece in a saturated solution of sodium or potassium hydroxide in an alcohol ("base bath"),[6] 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[citation needed], to give soluble silicates. Care should be taken using strongly alkaline solutions to clean fritted glassware, as this will degrade the frit over time.
More aggressive methods involving aqua regia (for removing metals from frits), piranha solution and chromic acid (for removing organics), and hydrofluoric acid baths are generally considered unsafe for routine use because of possible explosions and the corrosive/toxic materials involved.[6]
Chromic acid is not a preferred method if the glassware is to be used for the biological sciences, as chromate ions can implant themselves in the glass and produce anomalous results when it is subsequently used for cell cultures; to which the ions are toxic. A proprietary alternative known as NoChromix is available, which is essentially a sachet of largely ammonium persulfate and a smaller amount of surfactant. This is poured into a bottle of concentrated sulfuric. Like concentrated hydrogen peroxide, ammonium and sodium persulfate are strong oxidisers, yet they are not hydroscopic and are more stable. This allows them to be more easily stored and used. When mixed with concentrated sulfuric, they begin releasing oxygen, which can oxidise the carbonaceous dehydration products formed from organic residues by the sulfuric to carbon dioxide; 'burning' them off the glass. The rate of effervescence is slower than that of strong piranha solution, allowing more time for deposits to mechanically break up and for the mixture to be used before fully decomposing. This same method is used in some PCB etching tanks, where sodium persulfate (fine etch crystals) are combined with sulfuric acid to oxidise the copper surface and then make it water soluble as its sulfate.[citation needed] Gallery
A straight bore plastic stopcock without the female joint. Note its washer and nut system for attaching to its female joint.
A T-bore glass stopcock in a three way assembly. Two of the outlets end in plain hose adapters while the third ends in a male 14/20 ground glass joint. This stopcock is attached with an easily removed metal spring.
A double oblique bore glass three-way stopcock.
A single hole hollow glass stopcock held in place by vacuum.
A J. Young NMR tube attached to an adapter with a female 24/40 joint already greased. Note the hole resulting from the T-bore in the side of the PTFE plug.
A J. Young NMR tube from above looking down the hole that leads to the T-bore.
A Taper Joint Stopper with PTFE Sealing Ring. Optical transparency of the narrow sealing ring pressured by glass joint (right). Notes
Wikimedia Commons has media related to: Laboratory glassware
1. ^ "Hydrofluoric acid MSDS". J. T. Baker. Retrieved 2007-12-29.
2. ^ "Glass Frit Info". Adams & Chittenden Scientific Glass. Retrieved 2007-12- 29.
3. ^ Rob Toreki (2004-05-24). "Fritted Funnels". The Glassware Gallery. Interactive Learning Paradigms, Inc. Retrieved 2007-12-29.
4. ^ http://rsc.org/chemistryworld/Issues/2008/June/DrechselsBottle.asp
5. ^ "Suggestions for Cleaning Laboratory Glassware". Corning. Retrieved 2007-12-29. 6. ^ a b c J. M. McCormick (2006-06-30). "The Grasshopper's Guide to Cleaning Glassware". Truman State University.
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Laboratory equipment
Glassware Beaker
Boston round (bottle)
Büchner funnel
Burette
Condenser
Cuvette
Dean-Stark apparatus
Gas syringe
Graduated cylinder
Pipette
Petri dish Pycnometer
Ostwald viscometer
Büchner
Dewar
Erlenmeyer
Fernbach
Fleaker Flasks Florence
Retort
Round-bottom
Schlenk
Volumetric
Boiling
Ignition
Tubes NMR
Test
Thiele Thistle
Aspirator
Colony counter
Laboratory centrifuge Other Crucible
Eyewash
Glove box
Magnetic stirrer Meker-Fisher burner
Microtiter plate
Safety shower
Spectrophotometer
Stir bar
Stirring rod
Stopper
Scoopula
Vacuum dry box
See also: Instruments used in medical laboratories Categories:
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This page was last modified on 27 December 2012 at 12:51.
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