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 shovm in Fig. 26 
Fig. 26. Microscope with Large Stage for the Rapid Examination of Powdered 
Material. 
is of great assistance.^ 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 
^ Made by E. Leitz, Wetzlar and also by Nachet et Fils, Paris. 
