CH. V.] MALTOSE. 113 



B. The Disaccharides. 



Maltose is the disaccharide formed as the final product 

 of the hydrolysis of starch by enzymes, such as ptyalin, 

 diastase, etc. It is hydrolysed by boiling acids, and by 

 the enzyme maltase of the small intestine, to two molecules 

 of glucose. It exhibits well-marked reducing properties 

 towards Fehling's solution, but not towards Barfoed's. 

 It forms an osazone with phenyl-hydrazine acetate, which 

 is more soluble than glucosazone and which melts at 

 2o6C. Constitutionally it is glucose-a-glucoside. 



116. Preparation of Maltose. 



Weigh out 200 grams, of fine potato starch and divide it into 

 three approximately equal portions. Add 50 cc. of cold water to one 

 portion and stir until a uniform cream is obtained. Pour this 

 slowly into 1200 cc. of boiling water contained in an enamelled iron 

 vessel, stirring well during addition. Boil for a minute, stirring 

 all the time. Cool to 55 C. and add 2 cc. of a fresh malt extract 

 (see note i). 



The starch paste becomes liquified in a few minutes. Boil the 

 liquid again, and to it add the second portion of starch, which has 

 been stirred up with another 50 cc. of cold water. Cool to 55 C., 

 add 2 cc. of malt extract, and liquify as before. Boil again, add the 

 third portion of starch, and cool to 55 C. Add 40 cc. of malt extract, 

 and digest for 24 hours. Boil, filter, and evaporate in a porcelain 

 dish on a water bath until a fairly thick skim forms on the surface. 

 On another water bath heat 500 cc. of 95 per cent, alcohol in a flask 

 and pour it on to the hot syrupy solution, stirring well. The 

 maltose dissolves and the dextrin is precipitated, carrying down 

 with it a considerable percentage of the maltose. Connect the 

 flask to a reflux condenser (fig. 7) and heat on a boiling water 

 bath for 5 hours, repeatedly agitating the mixture. Allow the 

 mixture to cool thoroughly, and pour off the alcoholic solution 

 of maltose from the gummy residue of dextrine. Transfer 

 the alcoholic solution to a distilling flask connected with a 

 condenser and distil off the alcohol as completely as possible by 

 heating the flask on a water bath. Pour the thin syrupy residue 



