CARBOHYDRATES. 



33 



An instrument by means of which the extent of the rotation may 

 be determined is called a polariscope or polarimeter. Such an in- 

 strument designed especially for the examination of sugar solutions 

 is termed a saccharimeter or polarizing saccharimeter. The form of 



FIG. 3. 



C 



ONE FORM OF LAURENT POLARISCOPE. 



B, Microscope for reading the scale ; C, a vernier ; E, position of the analyzing Nicol 

 prism ; H, polarizing Nicol prism in the tube below this point. 



polariscope shown in Fig. 3, above, consists essentially of a long 

 barrel provided with a Nicol prism at either end (Fig. 4, below). 

 The solution under examination is contained in a tube which is 

 placed between these two prisms. At the front end of the instru- 

 ment is an adjusting eye-piece for focusing and a large recording 



FIG. 4. 



GO 



DIAGRAMMATIC REPRESENTATION OF THE COURSE OF THE LIGHT THROUGH THE LAURENT 

 POLARISCOPE. (The direction is reversed from that of Fig. 3, above.) 



a, Bichromate plate to purify the light ; b, the polarizing Nicol prism ; c, a thin 

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

 plane ; d, tube to contain the liquid under examination ; e, the analyzing Nicol prism ; 

 / and g, ocular lenses. 



disc which registers in degrees and fractions of a degree. The light 

 is admitted into the far end of the instrument and is polarized by 

 passing through a Nicol prism. This polarized ray then traverses 

 the column of liquid within the tube mentioned above and if the sub- 



4 



