102 THE CARBOHYDRATES 



Properties. 



Levulose separates from alcohol in hard rhombic crystals, 

 which have the composition CgHiaOg ; from concentrated 

 aqueous solutions, however, it crystallizes in needles with water 

 of crystallization 2C6H12O6 . H2O. It is fairly soluble in hot 

 absolute alcohol and ether, and may thus be separated from 

 other sugars which are insoluble in these solvents. Levulose 

 is strongly leevo-rotatory and exhibits slight muta-rotation ; its 

 rotatory power is very dependent on temperature, a^^" = — 93° 

 in a 10 per cent solution. 



Reactions. 



1. To a solution of levulose mixed with an equal volume 

 of concentrated hydrochloric acid a few grains of resorcin 

 are added. On warming, a deep red coloration results, and 

 finally a brown-red precipitate. The precipitate is soluble in 

 amyl alcohol, giving a deep red solution. 



This reaction is given by all keto-hexoses and by carbo- 

 hydrates such as cane sugar and raflfinose which give rise to 

 them on hydrolysis. 



2. Levulose gives the same reactions as dextrose with 

 salts of copper and picric acid. 



3. Levulose with milk of lime forms an insoluble com- 

 pound ; dextrose does not. 



4. Levulose gives with phenylhydrazine the same osazone 

 as glucose, namely glucosazone. 



5. With methylphenylhydrazine it gives, in alcoholic 

 solution, an osazone * crystallizing in needles ; m.p. 158-160°. 

 (Distinction from glucose and mannose.) 



Constitutioji. 



Fructose is a 2 keto-hexose whose constitution may be 

 represented by either of the two formulae : — 



* Neuberg : " Ber. deut. chem. Gesells.," 1902, 35, 961. 



