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The standard taper is the most common fitting. For example, a stopper marked as 24/40 is 24 mm in diameter at its widest part and 40 mm long on the tapered edge, which would fit into a flask with a 24/40 opening.Ĭonnections between pieces of glassware are made using a variety of ground glass joints including a standard taper, ball-and-socket, and O-ring. Rubber stoppers are sized by number, ranging from 000 – 10, whereas glass stoppers are sized by the diameter and length of the sealing section. While the seal is very good, glass-to-glass connections are known to seize, so joint grease (vacuum, Krytox, etc.) is often used to prevent this. Ground glass stoppers are used to seal flasks that have ground glass fittings. The downside of most flexible stoppers is that they break down over time, though newer Teflon stoppers are more robust but lack the physical flexibility. A variation of the stopper is the septum, which can be used to seal glassware and allows for easy access with a syringe needle. Stoppers can have anywhere from 0 – 3 holes, allowing for connections to tubing or inserting thermometers and stirrers. Stoppers are conical in shape and fit like a wedge into the glassware.
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Rubber and cork stoppers fit into standard glass necks, though cork is being phased out, and newer stoppers made of neoprene are taking over. Glassware can be sealed using a variety of stoppers, typically rubber, cork, or glass. When a piece of glass is marked as "TD", it is calibrated to accurately deliver the stated volume, whereas glassware with the "TC" marking only contains a specified volume, but it may not transfer to another vessel accurately. Thirdly, the notations "TD" or "TC" are used to indicate "to deliver" or "to contain", respectively. This is important because the density (and volume) of a liquid are dependent on temperature. The next piece of information is the temperature at which the glassware is accurate, typically 20 ☌. For one, an etched line or volume marking is typically located on volumetric glassware to indicate a volume. This accuracy is known to the user through a few different pieces of information on the glassware. Volumetric glassware, however, is considered very accurate. Standard laboratory glassware, like beakers and flasks, has a limited accuracy of measuring volume, typically ±5%. A greenish color is indicative of borosilicate impurities, whereas fused silica is optically clear and colorless. The easiest way to tell the difference between borosilicate glass and fused silica in the lab is to look down the long axis of a piece of glassware. Fused silica is chemically-pure silicon dioxide with no impurities and a very high melting point above 1,600 ☌. Fused silica, or quartz, is used in situations where glass needs to be heated above 450 ☌ or to be transparent to UV light. While borosilicate glass is thermally robust, the impurities found in borosilicate and standard glass lead to a limited temperature range and optical quality.
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The most common trade name for borosilicate glass is Pyrex, the same type of glass used in some kitchen bakeware.
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Made with an introduction of small amounts of boron, borosilicate glass has a very low coefficient of expansion, which prevents internal stresses. Borosilicate glass is used to solve this problem in the lab. It is good for many applications, but cracks under rapid heating and cooling applications due to expansion/contraction. Standard consumer-grade glass is known as "soda-lime" or "float" glass. Glass is ubiquitous in the chemistry laboratory, but not all glass is the same. While there are few rules about glassware, there are some best practices for use that set the groundwork for good techniques in the lab. While some labware is being supplemented with plastic or even everyday kitchen materials, glass is still the standard material by which laboratory work is done.
BEAKER USE PROFESSIONAL
Glassware is a regular appearance in the professional chemistry laboratory, because it has a relatively low cost, extreme durability, and specific levels of precision. Neal Abrams - SUNY College of Environmental Science and Forestry