04 



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. 



