MICROSCOPES FOR USE IN CHEMICAL LABORATORIES 69 



The coarse adjustment R by rack and pinion serves to roughly 

 focus both tubes at once; then each objective is focused sepa- 

 rately by means of the fine adjustment screw collars F, F 1 just 

 above the objectives. That really satisfactory results may be 

 obtained it is essential that both the sets of eyepieces and objec- 

 tives shall be paired, i.e., shall have been constructed for use 

 with a comparison microscope and be exactly equivalent in all 

 properties. The fields are flat, brilliant, and with careful illu- 

 mination and adjustment and a little practice most excellent 

 results can be obtained. The instrument is adapted to all 

 problems involving an exact comparison of size, structure or 

 symmetry of microscopic objects, especially where the structure 

 is so intricate as to render comparison and interpretation with 

 the ordinary single compound microscope exceptionally difficult 

 without recourse to photography. The value of the instrument 

 in all problems of forensic chemical microscopy is evident. 



A second type of comparison microscope 1 is provided with a 

 single eyepiece only, the field being divided into halves. As in 

 the previously described instrument, two microscope tubes are 

 attached to a single pillar and both focused together by rack 

 pinion. Attached to the tubes is a rectangular closed chamber 

 of the Inostranzeff type provided with two sets of totally reflect- 

 in prisms, thus yielding to a single eyepiece half the field of 

 view of each microscope. By means of a knob in the side of 

 the chamber one set of prisms may be shifted at will so as to cut 

 off the field of one instrument. 



In addition to a single fine adjustment, simultaneously affect- 

 ing both microscopes, each tube is provided with independent 

 fine adjustment collars just above the objectives. A single 

 stage with two openings carries two substages, each with an 

 Abbe condenser and with a mirror. The instrument may be 

 employed with polarized light, thus affording exceptional 

 opportunities for exact comparisons in the search for food 

 adulterants and in microchemical analysis. Since in this in- 

 strument we have a single ocular yielding a divided field, it is 

 possible to obtain photomicrographs, half the area of the circle 

 1 W. and H. Seibert, Wetzlar, Germany. Thorner, Chem. Ztg., 36, 781. 



