vj CARBOHYDRATES 53 



Expt. 44. Tests for laevulose. The following tests should be performed with a 

 0"2 % solution of laevulose in the same way as for glucose (see p. 50). 



(a) Moore's test. A positive result is obtained. 



(6) Tromrner's test. A positive result is obtained. 



(c) Fehling's test. Keduction takes place. 



{d) Osazone test. Note that the crystals are identical with those formed from 

 glucose. 



(e) a-Naphthol test (see ip. 4Q). A strong reaction is given. 



(/) Seliwanoff's test. To 5 c.c. of Seliwaiioff's solution (prepared by dissolving 

 0'05 gm. of resorcinol in 100 c.c. of 1 in 2 hydrochloric acid) add a few drops of 

 laevulose solution and boil. A red coloration and a red precipitate are formed. Add 

 a little alcohol and the precipitate forms a red solution (see p. 44). 



DiSACCHARIDES. 



These sugars are formed from the monosaccharides by condensation 

 with elimination of water. By boiling with dilute acids, or by the action 

 of certain enzymes, they are hydrolyzed into monosaccharides. The two 

 most important disaccharides found in plants are maltose and cane-sugar. 



Maltose. Maltose or malt-sugar, though it probably occurs in smaller 

 quantities than glucose and laevulose, is widely distributed in plant 

 tissues. It is formed in the hydrolysis of starch, and its relationships in 

 the plant to starch and to other sugars will be considered later. It is a 

 white crystalline substance soluble in water and alcohol. In constitution 

 it is a glucose-a-glucoside : 



CeHnOs— O— Cr-H 



H— C— OH 



I 

 CH2OH 



Maltose 



It reduces Fehling's solution ; but less readily than glucose. With 

 phenylhydrazine hydrochloride and sodium acetate it forms an osazone 

 (m.p. 206° C), which is more soluble than glucosazone and crystallizes 

 in broader flatter needles. Maltose is dextro-rotatory. 



Expt. 45. Tests for maltose. The tests a, 6, c and e, should be performed with a 

 0*2<^/o solution of maltose ; test d with a 2 7o solution (see also glucose, p. 50). 

 (a) Moore's test. A positive reaction is given. 

 (6) Trommer's test. A positive reaction is given. 

 (c) Fehling's test. Reduction takes place, but less strongly than with glucose. 



