MICROSCOPES FOR USE IN CHEMICAL LABORATORIES 63 



tors, while the range of the substage screw is long enough to 

 permit focusing the substage ring with auxiliary stage attached 

 in metallographic work, thus keeping the body tube with an 

 illuminator in line with the radiant. 



The milled heads of the stage centering screws have been made 

 much smaller and shorter than usual in order that they may 

 interfere less with manipulations on the stage and be less subject 

 to displacement. 



The revolving stage with circle graduated into degrees is 

 removable by merely unscrewing the centering screws, and then 

 lifting out the stage. This permits inserting into the substage 

 ring an auxiliary stage for use with thick objects, or opaque 

 objects, to be studied with a vertical illuminator (see Fig. 38, 

 page 88), or when preparations are to be heated with a tiny 

 flame. 



The polarizer PO consists of a Nicol prism set in a rotating 

 mounting graduated into degrees. A stud in the fixed part of the 

 mounting fits into a slot in the substage ring, thus insuring that 

 the polarizer mounting is always in the same relative position. 

 The analyzer, PA, a Thompson prism, fits over the eyepiece, 

 rotates, and is provided with a graduated circle. In the mount- 

 ing of the prism provision is made for adjustment in a vertical 

 direction so as to ensure a wide field of view with all oculars. 

 A slot in the collar in which the analyzer revolves engages a 

 stud St on the draw-tube of the instrument. The draw-tube 

 itself moves vertically only, thus if the polarizer and analyzer be 

 properly inserted and their graduated circles set at zero, the 

 prisms are crossed without further adjustment. The placing of 

 the analyzer over the eyepiece in a microscope for microchem- 

 ical analysis will be found to be much safer than the more con- 

 venient mounting sliding into the body tube, as in petrographic 

 instruments. When the instrument is to be much used in the 

 microscopy of foods a supplementary polarizer may be obtained 

 which fits into the ring below the Abbe condenser, thus allowing 

 the prism to be swung quickly aside without interfering with the 

 illuminating devices. 



Instruments made by other firms for chemical microscopy 



