Know your equipment: Ground Glass Joints

[Irons]

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 chemically- and heat-resistant corks or rubber bungs and glass tubes as joints which took time to prepare as well.
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http://en.wikipedia.org/wiki/Ground_glass_joint

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