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 
