78 THE CARBOHYDRATES 



Properties. 



Levulose separates from alcohol in hard rhombic crystals, 

 which have the composition C 6 H 12 O 6 ; from concentrated 

 aqueous solutions, however, it crystallizes in needles with water 

 of crystallization 2C 6 H 12 O 6 . H 2 O. 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 laevo- 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 

 alcohol, giving a deep red solution. 



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

 hydrates such as cane sugar and raffinose 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 methyl phenylhydrazine it gives, in alcoholic 

 solution, an osazone crystallizing in needles; m.p. 158. 

 (Distinction from glucose.) 



SORBOSE. 



Sorbose is a ketonic sugar produced by the fermen- 

 tative oxidation of the alcohol sorbite contained in the sap of 

 the mountain ash, Pyrus Aucuparia ; this sugar probably does 

 not exist as such in the plant, but is produced by oxidation as 

 described. 



GALACTOSE. 



This sugar is formed as a product of the hydrolysis pri- 

 marily of milk sugar, but also of the gums occurring in 



