CHAPTER XI 



Chemical Microscopy 



1. INTRODUCTION 



Great strides have been made in chemical microscopy since the works 

 of L. and A. Kofler. Application of the microscope to thermal analysis 

 provides the means to define and identify an organic compound and, 

 when a mixture is involved, to determine its composition. All phe- 

 nomena, concomitant with the temperature rise of a substance up 

 to its melting point, such as : sublimation, decomposition, birefringence, 

 polymorphic transformations and so forth, can be studied. This is 

 why the term "fusion methods" is frequently applied to operations 

 taking place during the temperature rise and the cooling of the specimen. 

 Lastly, microscopic methods require not only very little time but 

 small quantities of substance as well, usually a few milligrammes. 



2. HOT STAGE AND COLD STAGE 



The hot stage is the microscope element devised for application 

 of fusion methods. It is placed on the stage of a standard microscope 

 and designed for heating or cooHng the specimen ad libitum. 



Figure 11.1 shows the diagrammatic cross-section of the Kofler-type 

 hot stage. The apparatus is of cylindrical shape and has the size of 

 the microscope stage. The object is placed on the object-shde A and 

 encased in a cover-sHp. The object-slide is secured by the metal 

 frame B connected to the rod CC. The small threaded element V is 

 provided to rotate C about its axis thus shifting A in the direction CC . 

 The element V may rotate about a vertical axis so that, when shifting C 

 horizontally, A describes a circular motion centred upon V. These 

 two linked motions ensure that the specimen can be brought at any 

 point within the field of view. The upper and lower parts of the 

 heating-chamber are closed by the glass plates D and G, respectively. 



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