CARBOHYDRATES 257 



that carbohydrates are absent. A positive test, however, may 

 be due to other substances or to shreds of filter paper (cellulose). 



6. Heat a small portion of dry dextrose in a test tube. Note 

 the brown color and the odor of caramel. If a small amount of 

 sugar is heated in a test tube with concentrated potassium 

 hydroxide, a similar result is observed, the color and odor 

 of caramel appearing. This is known as Moore's test. 



7. Optical Activity. Carefully read the discussion of optical 

 activity in the text. The specific rotation of dextrose is +52.5 

 at 20 C. provided the concentration is not above 15%. With a 

 polariscope determine the rotary power of the dextrose solu- 

 tion furnished, and calculate the strength of the solution by 

 means of the following formula: 



oc . 100 



c = grams per 100 c.c. 



oc = observed rotation 



20 

 [ cc ] *" = specific rotation 



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 : 



,20 oc 100 



[OC] D -L V 



By referring to a table of specific rotations the sugar under 

 investigation can thus be identified. 



8. 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. 



