224 



ELEMENTARY CHEMICAL MICROSCOPY 



Any flat surfaced, stoppered container may serve as a hot 

 stage, as, for example, a small flat bottle. 



For temperatures above 150 C. the only convenient and uni- 

 versally applicable heating system is by means of an electric 

 current, resistance wire and suitable rheostat. The heating 

 coil in this case may consist of manganin, nichrome or platinum 

 wire. To obtain the best and most reliable results part of the 

 heating coil should be above the object being heated and part 

 below. 



Fig. 121 shows an electrically heated hot stage which has 

 been in use in the author's laboratory for several years. It 



FIG. 121. Apparatus for the Determination of Melting and Subliming Points. 



consists of a low cylinder of "Alberene stone" closed at the top 

 and bottom by thin glass, or by mica when high temperatures 

 are employed. The heating coil H, H consists of fine platinum 

 wire wound in fine coils. In the illustration A shows the Alberene 

 stone; B, brass guides for the object slide acting as cover; C, 

 adjustable wire fingers for supporting cover glasses, tiny crucibles, 

 " micro" retorts, etc.; D is a removable, thin brass diaphragm 

 cutting down the opening of the stage and serving as a radiator; 

 T, thermometer; PP, binding posts; M, mica or glass window 

 closing the bottom of the hot stage; and S, the object slide cover. 

 The method of inserting the hot stage for use in place of the rotat- 

 ing stage is shown in Fig. 122. By attaching an Abbe camera 

 lucida to the microscope tube and properly tipping the mirror, 

 the image of the scale of the thermometer may be so reflected 

 as to be seen alongside of the material whose melting point is 



