The sample in a capillary tube is held next to the bulb of a thermometer by eg a rubber band and placed in the ‘main’, straight part of the tube. The Thiele tube is basically a set tube with a side loop (see diagram). They come in at around £600.Ī cheaper alternative, that with care can still produce accurate results, is the Thiele tube. The one problem with the melting point apparatus described above is that of cost. The most commonly a heated metal block such as a Mel-Temp apparatus Thiele Tube The sample is loaded in a sealed capillary tube and the temperature gradually raised by means of an internal metal block. This is the most common piece of apparatus for determining melting point (as shown in the picture at the top of the page). There are a few ways of doing this Melting point apparatus The general method is to heat a sample indirectly by placing the prepared sample (either packed in a glass capillary or on a glass cover slip) in or on a heated medium and observing it, and the temperature, closely until melting is complete.
Pure samples usually have sharp melting points, for example 149.5-150☌ or 189-190☌ impure samples of the same compounds melt at lower temperatures and over a wider range, for example 145-148☌ or 186-189☌. You can find out more about melting points below. Determining the melting point of a compound is one way to test if the substance is pure and is often used to test samples made from organic synthesis (eg of aspirin or paracetomol).