THE CARBOHYDRATES. 



Like glucose, they are reducing agents, responding to Trommer's 

 and Fehling's tests. They also form osazones which, however, have 

 different melting points from the glucosazone. They do not fer- 

 ment with yeast, nevertheless they may be mistaken for reducing 

 sugars because of their other reactions. Arabinose, one of the 

 most common, can be obtained by boiling cherry-gum for 10 to 15 

 hours with 4 per cent, sulphuric acid. 



Prepare the arabinose from cherry-gum as indicated above, 

 neutralize and use for testing. 



44. Saturate 5 cubic centimeters of hydrochloric acid (30 per 

 cent.) with phloroglucin (about 25 milligrammes). Add to this 

 the urine or solution which is to be tested for pentoses and heat. 

 The presence of pentoses is indicated by a red color and this shows 

 absorption bands between D and E of the spectrum. Glucuronic 

 acid gives a similar result. 



45. Repeat the test as in the last experiment substituting 

 orcin for phloroglucin. Pentoses produce a green color. Glu- 

 curonic acid does not act in this manner. 



BEACTIONS OF THE CARBOHYDRATES. 



