Melting point tubes open both ends

The heating of the vessels is accomplished by means of a small bath or a micro-Bunsen burner. The vessel can be clamped at such a distance from the burner that the contained liquid boils gently under reflux. Smooth boiling is ensured by the addition of 1-2 minute pieces of unglazed porcelain, or of a short piece of melting-point tubing open at both ends. 

Sometimes you may get a supply of tubes that are open on both ends You don t just use these as is. Light a burner, and close off one end, before you start. Otherwise your sample will fall out of the tube (see Closing Off Melting Point Tubes, following). 

If you have melting point tubes that are open at both ends and you try to take a melting point with one, it should come as no surprise when your compound falls out of the tube. You ll have to close off one end, to keep your sample from falling out (Fig. 32). So light a burner and get a stiff small blue flame. SLOWLY touch the end of the tube to the side of the flame, and hold it there. You should get a yellow sodium flame, and the tube will close up. There is no need to rotate the tube. And remember, touch— just touch—the edge of the flame, and hold the tube there. Don t feel you have to push the tube way into the flame. 

Capillary tubes (melting point capillaries open on both ends)... 

Heat the middle of an open-ended melting point tube at the tip of the hot flame of a microburner until it begins to sag. If the melting point tube is sealed at one or both ends, carefully break off the sealed end(s) wearing gloves for protection. 

Apparatus Use any suitable commercial or other apparatus. Use melting-point capillary tubes—id, 1 mm od, 2 mm length, 50 to 80 mm and open at both ends. 

Capillary tubes for melting point measurement are available commercially and are supplied open at both ends or closed at one end or closed at both... 

By capillary action, molten fat sample is drawn into the tube, which is open at both ends. The fat is solidihed by chilling and then melted in water at a regulated rate of increase in temperature. The temperatures at which the fat shps and appears clear in the liquid state are noted as its slip/melting points or melting range. 

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