CARBOHYDRATES. 35 



CH 2 OH 



UEVULOSE, (CHOH) 3 . 



A 



H 2 OH 



As already stated, laevulose, sometimes called fructose or fruit 

 sugar, occurs widely disseminated throughout the plant kingdom 

 in company with dextrose. Its reducing power is somewhat weaker 

 than that of dextrose. Laevulose does not ordinarily occur in the 

 urine in diabetes mellitus, but has been found in exceptional cases. 

 With phenylhydrazine it forms the same osazone as dextrose. With 

 methylphenylhydrazine, laevulose forms a characteristic methyl- 

 phenyllaevulosazone. 



(For a further discussion of Isevulose see the section on Hexoses, 



p. 22.) 



EXPERIMENTS ON L^VULOSE. 



i ii. Repeat these experiments as given under Dextrose, pages 



23-31- 



12. Seliwanoff's Reaction. To 5 c.c. of SeliwanofFs reagent 1 

 in a test-tube add a few drops of a Isevulose solution and heat the 

 mixture to boiling. A positive reaction is indicated by the produc- 

 tion of a red color and the separation of a red precipitate. The 

 latter may be dissolved in alcohol to which it will impart a striking 

 red color. 



If the boiling be prolonged a similar reaction may be obtained 

 with solutions of dextrose or maltose. 



13. Borchardt's Reaction. To about 5 c.c. of a solution of 

 laevulose in a test-tube add an equal volume of 25 per cent hydro- 

 chloric acid and a few crystals of resorcin. Heat to boiling and 

 after the production of a red color, cool the tube under running 

 water and transfer to an evaporating dish or beaker. Make the 

 mixture slightly alkaline with solid potassium hydroxide, return it 

 to a test tube, add 2-3 c.c. of acetic ether and shake the tube vig- 

 orously. In the presence of Isevulose, the acetic ether is colored 

 yellow. (For further discussion of the test see Chapter XIX.) 



14. Formation of Methylphenyllaevulosazone. To a solution 



1 Seliwanoff's reagent may be prepared by dissolving 0.05 gram of resorcin 

 in 100 c.c. of dilute (1:2) hydrochloric acid. 



