CARBOHYDRATES AND RELATED BODIES. 



39 



may be safely added. If added too rapidly the end point may be over- 

 looked and the sugar content made to appear too low. 



Polarization Tests and the Use of the Polariscope. This is the proper 

 place to show the applications of the polariscope in the examination of 

 sugars and other substances. For a description of the various forms of 

 polariscopes and discussion of the optical principles involved in their con- 



FIG. i. A common form of Laurent polariscope. The polarizing prism is 

 situated in the tube below H, the analyzer at E, B is the reading microscope 

 and C a vernier. 



struction the reader is re/erred to the author's translation of Landolt's 

 work, " The Optical Rotation of Organic Substances and its Practical 

 Applications," but a few words of elementary explanation may be in order 

 here. A simple form of polarimeter in common use is shown in the illus- 

 trations. 



In the polariscopes in common use for general scientific studies homo- 

 geneous yellow light is employed and this is first polarized by passing 

 through a specially designed prism in the front part of the instrument. This 



BO 



f s 



FIG. 2. This represents the course of the light through the Laurent polari- 

 scope, the direction being reversed, however, from that of the last figure, a 

 is a bichromate plate to purify the light, b the polarizing Nicol, c a thin 

 quartz plate covering half the field and essential in producing a second 

 polarized plane, d the tube to contain the liquid under examination, e the 

 analyzing Xicol and / and g the ocular lenses. 



