Ground glass joint
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Ground glass joints are used in laboratories to quickly and easily fit leak-tight apparatus together from commonly available parts.
Conically tapered joints
The most common form, comes in various sizes: Internationally the ISO sizes used 14/23, 19/26, 24/29, 29/32 very common in research laboratories, with 24/29 the most common. In the US the ASTM sizes are used with common sizes being 14/20, 19/22, 24/40 and somewhat 29/42, with 24/40 the most common.
Often encountered in rotary evaporators, in the distillate collecting flask. Doesn't require greasing.
One of the worst thing that can happen to two connected ground glass joints is to get stuck, usually due to not being (well) greased, exposure to a strong base, etc.
One way to solve this problem is to heat the external joint (female) with a heat gun to around 500 °C and then gently tap it to release it. This method can also work for joints where a strong base has glued the joints, though if the corrosion is severe, it may not work.
On occasion, a simple gentle but firm tap with a wooden stick may work.
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