34 



PHYSIOLOGICAL CHEMISTRY. 



stance is optically active the plane of the polarized ray is rotated to 

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

 dextro-rotatory and those rotating it to the left Icevo-rotatory. 



Within the apparatus is a disc which is so arranged as to be 

 without lines and uniformly light at zero. Upon placing the opti- 



FIG. 5. 



POLARISCOPE (SCHMIDT AND HANSCH MODEL). 



cally active 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 and uniformly light." The differ- 

 ence between this reading and the zero is a or the observed rotation 

 in degrees. 



Polarizing saccharimeters are also constructed by which the per- 

 centage of sugar in solution is determined by making an observa- 

 tion and multiplying the value of each division on a horizontal slid- 

 ing scale by the value of the division expressed in terms of dex- 

 trose. This factor may vary according to the instrument. 



