3 8 PHYSIOLOGICAL CHEMISTRY. 



color. To differentiate between these bodies make a spectroscopic 

 examination and look for the absorption band between D and E 

 given by pentoses and glycuronic acid. Differentiate between the 

 two latter bodies by the melting-points of their osazones. 



Compare the reaction with that obtained with galactose (page 36) . 



2. Orcin Test. Repeat i, using orcin instead of phloroglucin. 

 A succession of colors from red through reddish-blue to green 

 is produced. A green precipitate is formed which is soluble in 

 amyl alcohol and has absorption bands between C and D. 



3. Phenylhydrazine Reaction. Make this test on the arabinose 

 solution according to directions given under Dextrose, 3 or 4, 

 pages 24 and 25. 



CH 2 OH 



XYLOSE, (CHOH) 3 . 

 CHO 



Xylose, or wood sugar, is obtained by boiling wood gums with 

 dilute acids as explained under Arabinose, page 37. It is dextro- 

 rotatory and forms an osazone. 



EXPERIMENTS ON XYLOSE. 

 1-3. Same as for arabinose (see page 37). 



RHAMNOSE, C 6 H 12 5 . 



Rhamnose or methyl-pentose is an example of a true carbohydrate 

 which does not have the H and O atoms present in the proportion 

 to form water. Its formula is C H 12 O 5 . It has been found that 

 rhamnose when ingested by rabbits or hens has a positive influence 

 upon the formation of glycogen in those organisms. 



DISACCHARIDES, C^E^Ai- 



The disaccharides as a class may be divided into two rather dis- 

 tinct groups. The first group would include those disaccharides 

 which are found in nature as such, e. g., sucrose and lactose 

 and the second group would include those disaccharides formed in 

 the hydrolysis of more complex carbohydrates, e. g., maltose, and 

 iso-maltose. 



