Melting point determination test

The procedure known as the mixed melting point determination, whereby the melting range of a solid under test is compared with that of an intimate mixture of equal parts of the solid and an authentic specimen of it, may be used as a confirmatory identification test. Agreement of the observations on the original and the mixture usually constitutes reliable evidence of chemical identity. 

If the compound dissolved in the hot solvent and crystallized on cooling, the crystals should be obtained and their melting point determined in order to see whether purification has been effected. This may be done by collecting the crystals on a Hirsh or other type of microfunnel. However, the following technique is more convenient. A circle of filter paper about 13 mm in diameter is cut out with a well-sharpened cork borer. This is placed over the mouth of the test tube, and a hollow glass tear (Fig. 2-20) is placed over the filter paper. A retaining wire made from 20-gauge nichrome wire is placed over the tear, and a... 

Melting point determination is a test that is included in most pharmacopoeias. Other thermal... 

The standard test for an aldehyde or ketone is that they both form orange crystalline precipitates with 2,4 dinitrophenylhydrazine solution (Figure 10.79a). The precipitate can be recrystallized and its melting point determined (Figure 10.79b). Knowing the melting point of the crystals enables us to identify the particular aldehyde or ketone tested. 

If a solution of the tested substance forms a precipitate on the addition of a 2,4-dinitrophenylhydrazine solution in 2N HCl, this represents a detection of the presence of a carbonyl compormd. If the precipitate is isolated and purified by crystallization and its melting point determined, identification has been made, because on comparison with the published data or on measuring the mixture melting point with an authentic sample we can determine the identity of the original substance. 

Obtain a sample of wax representative of the shipment to be tested. From each test unit obtain a portion of wax weighing at least 25 g for each melting point determination. 

---