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The Preparation of Microscope Slides 



Fig. 91. Simple radiant-heat embedding oven. Height of the hood should be adjusted 

 until the wax is melted for about one-half its depth. 



required are filled with wax, placed under the reflector, and the current 

 is turned on. After a little while, it will be observed that the absorbed 

 heat has melted the wax. The wax may be melted only at a small surface 

 layer, throughout the entire vial, or, as is required, in the upper two-thirds 

 of the vial. If this last is not achieved, the height of the lamp must be 

 varied until after an hour or two each of the vials contains about one- 

 third of unmolten opaque wax at the bottom and two-thirds of the clear 

 molten material above. Thus, when the object is placed in one of these 

 vials, it will drop until it reaches the solidified layer, where it will remain 

 in contact with molten wax at exactly the melting point of the wax. It is 

 obvious that the room in which this operation is to be conducted must 

 be at a fairly constant temperature and must be relatively free of drafts, 

 but only a very large volume of embedding work justifies the purchase of 

 an expensive thermostatically controlled oven. If such an oven is to be 

 purchased, it is highly desirable to avoid one in which the heat is distrib- 

 uted by convection. The oven shown in Fig. 92, in which a circulating fan 

 continuously moves the air and thus maintains a uniform temperature 

 throughout the whole oven, is infinitely to be preferred. It is the high cost 

 of such circulating air ovens that leads the author to believe that much 



