go ELEMENTARY CHEMICAL MICROSCOPY 



The specimen to be mounted is laid upon a piece of lens paper, 

 polished side down upon the bed piece. The collar is then raised 

 or lowered the proper amount and an object slip carrying a bit 

 of plasticine is inverted over the preparation and pressed down 

 until each end touches the circumference of the collar. The slip 

 may now be lifted off, carrying with it the specimen imbedded 

 in the plasticine or wax. Laid upon the stage of the microscope, 

 the polished surface of the specimen will be in a plane normal to 

 the optic axis of the microscope. 



Metallurgical Microscopes. The extraordinary interest in 

 the microscopic study of metals and alloys within the last ten 

 years and the astonishing development of theories relative to 

 their constitution and structure, followed by the application of 

 this information to the mechanic arts, has led to the design of 

 special forms of microscopes to facilitate the study of the many 

 different problems arising in the metallurgical industries. In 

 all these special types of microscopes we have to deal with 

 compound microscopes, having permanently attached, between 

 ocular and objective, a vertical illuminator, usually of the prism 

 type. 



Since the etched surfaces of metals ordinarily yield images of 

 such intricacy that notebook sketches become impracticable, 

 recourse must be had to photography. Most metallurgical 

 microscopes therefore include as an integral part of the in- 

 strument a photographic camera, and when thus provided 

 they are often known as metallographic microscopes or metallo- 

 graphs. 



In order that the structure of an alloy may be studied it is 

 essential: (i) that a small area shall be ground to a plane surface, 

 polished and etched; (2) that this plane surface shall lie normal 

 to the optic axis of the microscope; (3) that the area of this 

 plane shall be so situated with reference to surrounding parts 

 that the objective may be brought sufficiently close to it to 

 be focused. 



Were the preparation to be laid upon the stage of an ordinary 

 microscope it would have to be thin and to have another sur- 

 face ground parallel to the etched surface. To avoid these 



