CARBOHYDRATES 



33 



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 coluirm of liquid within the tube mentioned above and 

 if the substance is optically active the plane of the polarized ray is 



FIG. 7. DIAGRAMMATIC REPRESENTATION OF THE COURSE OF THE LIGHT THROUGH THE 



LAURENT POLARISCOPE. (The direction is reversed from that of Fig. 6, p. 31.) 

 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 t 

 tube to contain the liquid under examination; e, the analyzing Nicol prism;/ and g, ocular 

 lenses. 



rotated to the right or left. Bodies rotating the ray to the right are 

 called dexro-rotatory and those rotating it to the left lew-rotatory. 



Within the apparatus is a disc which is so arranged as to be without 

 lines and uniformly light at zero. Upon placing the optically active 



FIG. 8. POLARISCOPE (SCHMIDT AND HANSCH MODEL). 



substance in position, however, the plane of polarized light is rotated 

 or turned and it is necessary to rotate the disc through a certain number 

 of degrees in order to secure the normal conditions, i.e., " without lines 



3 



