Analytical techniques for studying and characterizing polymorphs

Since polymorphs represent different crystal structures essentially every physical or chemical property may vary among the polymorphic structures of a material. A consequence of this is the fact that virmally any technique that measures the properties of a solid material may in principle be used to detect polymorphism and to characterize the similarities and difference among polymorphic structures. Some techniques are more sensitive to the differences in crystal structure or molecular environment, as opposed to molecular structure, and in many cases these are to be preferred in detecting and characterizing polymorphs. 

Hot stage microscopy provides a rapid method for screening substances for the existence of polymorphism. In spite of the utility of this technique, it has not enjoyed the widespread use it deserves. Microscopy was much ignored during the 

The most general use of the microscope for the study of polymorphism is simply for observing the homogeneity or diversity of a crystalline sample. Variations in size, shape or colour may indicate the presence of polymorphism and the need for further examination (see, for instance Fig. 3.2). As noted in Section 2.4.1, differences in crystal habit are not necessarily indicative of polymorphism. Further physical characterization of the individual crystals may involve measurements such as optical constants (Hartshorne and Smart 1960, 1964 Wahlstrom 1969 McCrone et al. 1978) or interfacial angles (Winchell 1943 Porter and Spiller 1951 Terpstra and Codd 1961). 

The systematic use of the hot stage microscope employing mainly the Kofler hot stage was originally described in the book by Kofler and Kofler (1954) (the founders 

The determination of the index of refraction of the melt (a procedure readily performed on the microscope (McCrone 1957 Kuhnert-Brandstatter 1971)) can serve as 

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