MOUNTING OBJECTS DRY. 285 



care be taken to roughen the surfaces of contact, the 

 tendency to leak when filled with fluid will be much 

 reduced. A considerable number of cells of various 

 diameters and depths should be made at one sitting, and a 

 stock of old cells always kept on hand. If new ones are 

 used they often turn out unsatisfactorily. 



Large cells may be made of four separate walls of glass 

 all ground together to one level, cemented by their corners 

 to the glass slide with marine glue. In using marine glue 

 the surfaces to be united should be heated very hot, the 

 marine glue applied to the edges, and kept firmly pressed 

 together until set. They may then be further heated in 

 the bath, Fig. 237, for twelve hours. 



In passing now to the mounting of objects, the reader 

 will see the impossibility of describing how any particular 

 object or class of objects may be successfully mounted ; 

 which is the best of the several methods can only be 

 discovered in actual practice, and if the salient points in 

 each method of mounting be described, the student will 

 no doubt learn much that will help him with other 

 subjects. 



For this reason the mounting of objects has been divided 

 into three sections 



1. Mounting dry. 



2. Mounting in gum resins. 



3. Mounting in aqueous media. 



DRY MOUNTING. In treating of dry mounting we may 

 so subdivide the work as to show the isolated operations 

 upon which success depends, and in doing so, the student 

 will see the importance of thoroughly understanding the 

 why and the wherefore of each operation. These may be 

 described as follows : 



Cleaning the Specimens. This is a section upon which a 



