Laboratory Glassware
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This week we are launching Wikivoyage . Join us in creating a free travel guide that anyone can edit. Laboratory glassware From Wikipedia, the free encyclopedia Jump to: navigation, search This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (February 2011) 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.