Melting point capillary tube
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A melting point capillary tube, also called melting point determination tubes or just capillary tube, is a very thin tube of glass used to determine the melting point of solids.
Melting point capillary tubes are thin and short (70-100 mm × 0.8 mm × 1 mm) borosilicate glass tubes, open at both ends.
In order to use them to determine the melting point of solids, you must first seal it at one end, which can be done by heating one end with a flame. Any flame can be used, even a simple disposable lighter is enough to seal one end of the tube.
Melting point capillaries can be bought in bulk from lab suppliers and they're quite cheap.
DIY capillary tube
You can make a simple capillary tube by heating a glass rod in a gas torch and then stretching the softened glass until you reach the desired length and thinness. Scratch the capillary using an ampoule cutter and then snap it to cut it whole.