Crystallization freezing-point determination

The temperatures of crystallization were determined by observing the rate of cooling in the presence of nuclei of the phases, which were expected to crystallize. The crystallizations in the absence of nuclei are usually difficult, the supercooling being considerable. This is especially the case with the crystallization of the compounds and of sulphuric acid. Therefore a small amount of crystals was left by slow melting of the crystallized mixtures to act as nuclei, and the cooling then resumed in order to obtain the accurate freezing point. 

At very low temperatures carbon disulphide solidifies to a crystalline mass which melts at —112-97° C.7 The crystallisation may be accompanied by the emission of small sparks.8 At —185° C. the crystals are tetragonal.9 The heat of fusion, deduced from determinations of the freezing-points of dilute solutions in certain organic solvents,10 is 660 calories. The fusion curve showing the connection between pressure and melting-point has been determined.11... 

It would also be helpful to run an infrared spectrum of the sample to determine what functional groups are present. This will help in the selection of a stationary phase. Cooling the sample can be easily accomplished, and, if any solids crystallize, they can be easily removed, thus providing a simple separation. Remember that freezing points are not necessarily related to boiling points, and they often represent a simple way to clean up a complex sample. 

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