MICROSCOPES FOR USE IN CHEMICAL LABORATORIES 61 
and analyzer are in their proper places the planes of vibration 
of these prisms will be crossed without the necessity of experi¬ 
mental adjustment. 
7. The instrument must be provided with a mirror, plane, on 
one side, concave on the other, of as large diameter as possible, 
which permits turning over from plane to concave side when 
the microscope is in a vertical position without the necessity of 
tipping the pillar. The mirror should be mounted on a swing¬ 
ing bar to provide very oblique light and it is desirable that the 
bar have an extension arm in order that the mirror may be swung 
to give oblique light above the stage. 
8. At least two of the oculars (a high power and a low power) 
must be fitted with cross-hairs and stud fitting into a notch or 
slot in the upper end of the draw-tube. 
9. The objectives should be of exceptionally long working 
distance and in combination with the eyepieces should yield a 
magnification of from 15 or 20 diameters to 300 or 350 diameters 
for ordinary work. 
10. The instrument should be of as simple construction as 
possible and should permit the easy and inexpensive replace¬ 
ment of parts damaged through accident. 
TYPES OF MICROSCOPES FOR MICROCHEMICAL INVESTIGA¬ 
TIONS. 
Instruments for General Use. — A microscope which con¬ 
forms very closely to the specifications given above is shown 
in its latest model in Fig. 25. This instrument has been con¬ 
structed after specifications of the author^ to meet most of 
the problems arising in chemical laboratories in which a micro¬ 
scope may be employed. In this model an attempt has been 
•made to provide as compact an instrument as possible, having 
an exceptionally great distance between the optic axis and the 
arm, thus providing sufficient manipulative space for large ob¬ 
jects, cells, etc.; the range of the body tube is also sufficient to 
permit even very low powers to be used with vertical illumina- 
1 Chamot, J. Applied Micros., 2 (1899) 502. Manufactured by the Bausch 
& Lomb Optical Co., Rochester, N. Y. 
