114 THE CARBOHYDRATES. [CH. V. 



into a beaker and allow to cool. Add a little crystalline maltose 

 and allow to stand for 24 hours in a cool place. The syrup should 

 set to a semi-solid crystalline mass. Spread this on a porous earthen- 

 ware plate to dry. 



Recrystallisation. 



Weigh the solid, add one-fourth of its volume of water, and 

 heat on the water bath until a syrup is formed. For every cc. 

 of water taken add 10 cc. of hot 88 per cent, alcohol. Filter. Cool, 

 add a little crystalline maltose, and allow to stand for about 2 days. 

 Filter on the pump, wash with a little 95 per cent, alcohol, and dry 

 on a porous plate. 



NOTES. i. Preparation of malt extract. Mix 40 grams, of finely ground 

 pale dried malt with 100 cc. of cold water. Shake well, and allow to stand for 

 lour hours. Filter. 



2. It is easier to prepare a strong solution of starch by using soluble 

 starch (see p. 391). In this case boil 1200 cc. of water, stir 200 grams, of the 

 soluble starch with 200 cc. of cold water, and pour this slowly into the water, 

 kept hot on a boiling water bath. Cool to 55 C. and add 40 cc. of the malt 

 extract. 



Use a i per cent, solution for the following exercises : 



117. Repeat Exs. 95, 99 and 100. The reactions are indis- 

 tinguishable from those of glucose. 



118. Repeat Exercise 98. A reduction is generally obtained. 

 (Distinction from glucose.) 



119. Repeat Exercise 102, using 12 drops of the 20 per cent, 

 copper sulphate for the first trial. It will be seen that the maltose 

 has a reducing power of about 60 per cent, that of a glucose solution 

 of the same strength. 



120. Repeat Exercise 103, using 20 drops of the copper sul- 

 phate for the first trial. The reducing power of the solution has been 

 markedly increased, owing to the hydrolysis of the maltose to 

 glucose. (Distinction from glucose.) 



121. Repeat Exercise 101. A reduction is not usually ob- 

 tained. (Distinction from glucose.) 



NOTE. It must be remembered that the glucose solution employed was 

 0-2 per cent. Two cc. of this can only reduce 4 to 5 drops of 20 per cent, 

 copper sulphate (see Ex. 102). So that, though the i per cent, maltose solu- 

 tion employed exhibits strong reducing powers towards alkaline copper 



