![]() Do not heat so vigorously that the entire sample boils away. The purpose of this step is to expunge the air originally present in the capillary tube and replace it with the sample's vapor. Continue heating until a vigorous stream of bubbles emerges from the tip of the capillary tube (Figure 6.25d), such that individual bubbles can barely be distinguished.Studies of this method\(^7\) have determined that it is best to heat the oil gently and in a continual manner, as stopping and starting have caused the results to suffer.It is okay to continue heating a Thiele tube if bubbles are seen. If the oil is not subsequently changed, the sample may boil when heated in the tube. In this method, the rubber band occasionally breaks causing the sample to fall into the oil and contaminate it. Although bubbles should not be seen in the Thiele tube as it warms, they commonly are seen if the tube had been used previously for boiling point determinations.This method is an excellent way to indirectly and slowly heat the sample. The cooler, denser oil will sink, thereby creating a current as shown in Figure 6.25c). If the melting point of the mixture is the same as that of the known compound, then the known and the unknown are most likely identical. A small portion of a known compound, whose melting point is known, is mixed with the unknown compound. As the oil warms and becomes less dense, it will rise and travel up the triangular portion of the tube. A mixture melting point is useful in determining the identity of your unknown compound. Heat the oil gently on the side arm of the Thiele tube with a microburner if available, or Bunsen burner using a back and forth motion (Figure 6.25c).The thermometer should not touch the sides of the glass, and if it does it should be clamped in such a way that it no longer touches. The rubber band should be higher than the top of the mineral oil (Figure 6.25b), keeping in mind that the oil may expand somewhat during heating. Place the rubber stopper and thermometer assembly into the Thiele tube, adjusting the height so that the sample is midway (if possible) inside the tube (Figure 6.25a).Insert a capillary tube into the sample (the same type that is used for melting points), open end down and sealed end up (Figure 6.24d).įigure 6.25: a) Insertion of the assembly into the Thiele tube, b) Rubber band is above the oil, c) Heating, d) Vigorous bubbling of sample. ![]() The Thiele tube may also be used to determine boiling points, by using a liquid sample instead of a solid sample.\( \newcommand\) of sample (Figure 6.24c). By using different oils, different temperature ranges can be reached and used to determine melting points. The sample is placed in the opening in a capillary tube alongside a mercury thermometer and allowed to be heated by the oil as it circulates through the Thiele tube. The control panel might have buttons that allow the start and end of the melting point range to be recorded.Ī Thiele tube is a glass instrument that is filled with oil that is heated by using an open flame. Some machines have several channels, which permit more than one sample to be tested at a time. The temperature range that is determined can then be averaged to gain the melting point of the sample being examined.Īpparatuses usually have a control panel that allows the starting and final temperatures, as well as the temperature gradient (in units per minute), to be programmed. The operator of the apparatus records the temperature range starting with the initial phase-change temperature and ending with the completed phase-change temperature. Dynalon DMP100 Digital Melting Point Device. DWK Life Sciences (Kimble) View Product Details. The sample is then heated, either by a heating block or an oil bath, and as the temperature increases, the sample is observed to determine when the phase change from solid to liquid occurs. DWK Life Sciences KIMBLE ® KIMAX ® Melting Point Capillary Tube, Sealed at One End. While the outward designs of apparatuses can vary greatly, most apparatuses use a sample loaded into a sealed capillary ( melting-point capillary), which is then placed in the apparatus. Some types of melting-point apparatuses include the Thiele tube, Fisher-Johns apparatus, Gallenkamp (Electronic) melting-point apparatus and automatic melting-point apparatus.
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