220 PHYSIOLOGICAL CHEMISTRY 



tion furnished, and calculate the strength of the solution by 

 means of the following formula: 



oc 100 



c = grams per 100 c.c. 

 observed rotatk 

 specific rotation 



oc = observed rotation 



20 

 D 



L = length of observation tube in decimetres 



Record the observed rotation. By means of the formula calcu- 

 late the weight of dextrose per 100 c.c. 



If the weight of an unknown sugar in 100 c.c. of solution is 

 known, the specific rotation may be calculated by observing the 

 rotation, and substituting in the following formula : 



r n 20 ex'' 100 



[oc] D -LT c- 



By referring to a table of specific rotations the sugar under 

 investigation can thus be identified. 



x. Fermentation. The fermentation test is useful in detect- 

 ing the presence of many sugars. If dry yeast is used, the yeast 

 solution must be "set" the day before using and kept warm at 

 least over night. Compressed yeast may be used immediately. 

 Gently rub up the yeast with the sugar solution to be tested, 

 making a homogeneous mixture. 



Fill an Einhorn fermentation tube with this mixture. Make 

 sure that all air is removed from the tube. When the tube is 

 full, pour out most of the liquid from the bulb. Otherwise it will 

 overflow into the incubator in case fermentation takes place. 

 Label the tube with your name and the kind of sugar under ex- 

 amination and place in an incubator at 38-40 C. until the next 

 class period. Eemove the tube and add 3-4 c.c. cone, sodium 

 hydrate from a pipette in such a way that it will enter the upright 

 portion of the tube. Be careful that the gas in the tube does 



