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 1 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. 



