64 



ELEMENTARY CHEMICAL MICROSCOPY 



differ but little from that shown in the illustration. It has, 

 therefore, been thought unnecessary to picture them here. 



Microscopes for Special Purposes. When large samples of 

 powdered material are to be investigated, as in the examination 

 of dry, powdered or granulated foods, drugs, etc., for adulter- 

 ation, a microscope with large stage of the type shown in Fig. 26 



FIG. 26. Microscope with Large Stage for the Rapid Examination of Powdered 



Material. 



is of great assistance. 1 The material is thinly spread out upon 

 the plate glass stage, and the microscope is made to pass by 

 means of the screws S and R over the entire area covered by 

 the material. A very low power L is first employed until some 

 particle is found, needing to be studied more carefully. The par- 

 ticle is centered under the lens, L is then removed and the com- 

 pound microscope M slipped in place in the same slot previously 

 occupied by L. The particle in question now falls under the 

 compound microscope. This type of microscope primarily in- 

 tended for the examination of large sections of the brain will 



1 Made by E. Leitz, Wetzlar and also by Nachet et Fils, Paris. 



