40 ANALYTICAL PROCESSES. 



The specific rotatory power of a substance is the 

 amount of rotation of the plane of polarized light, in 

 angular degrees, produced by a solution containing 

 one gram of the substance in one c. c, examined in a 

 column one decimeter long. 



It is expressed by the following formula in which 



5 is the specific rotatory power for light of wave 

 length corresponding to the D line of the spectrum 

 (sodium flame). 



a is the angular rotation observed, 



c is the concentration of the solution (weight 

 in grams, in lOO c. c. of the liquid) and 



/ is the length of the tube in decimeters. 

 lOO a 



Calculation of the amount of sugar corresponding 

 to the observed rotation may be made by substitution 

 in the formula. 



The sodium flame is most conveniently obtained by 

 means of a bead of sodium carbonate, on platinum 

 wire, heated in the flame of the Bunsen burner. 



The specific rotatory power of milk sugar is unaffect- 

 ed by the concentration within the limits encountered 

 in ordinary analytical work. It is slightly affected by 

 temperature, being decreased by about .042 angular 

 degree for each successive rise of one^ ^degree. The 

 specific rotatory power at 68° F. is 52.5° when obsev- 

 ed by the sodium flame. 



Birotation. — When freshly dissolved in cold water, 

 milk sugar shows a higher rotation than that given 



