VOLUMETRIC ESTIMATIONS 97 



sugars are precipitated as lead compounds. Filter off and 

 wash the precipitate ; suspend the precipitate in water and 

 pass through it a current of carbon dioxide. The lead com- 

 pound of glucose alone is decomposed, and the glucose goes 

 into solution. Filter off and thoroughly wash the levulose 

 lead compound, and then suspend it in water and decompose 

 it with sulphuretted hydrogen. 



Similarly, should these two sugars be mixed with cane 

 sugar, the latter, on the addition of ammoniacal lead acetate, 

 remains in solution, and thus is easily separated. 



Inasmuch as this method is somewhat tiresome, the follow- 

 ing methods may be followed whenever possible : 



GLUCOSE AND SUCROSE. 



1. Take 100 c.c. of the mixture and titrate with Fehling's 

 solution. 



2. Invert 100 c.c. of the mixture by the method given, 

 and titrate. 



The first operation gives the amount of glucose = a. 

 The second operation gives the original amount of glucose 

 together with that due to the inversion of the cane sugar = b. 



.'. (b - a) x -95 = sucrose. 

 GLUCOSE AND MALTOSE. 



Proceed exactly as for glucose and sucrose : " 



a = amount of sugar before inversion. 

 b = amount of sugar after inversion. 



From the reasons already given under maltose, it follows 

 that 



(6 -a) x 2*32 = maltose, 

 and a - (maltose x '62) = glucose. 



CANE SUGAR AND MALTOSE. 



Cane sugar is inverted by citric acid, white maltose is not ; 

 this fact may be made use of in the estimation : 



I. Add to 100 c.c. of the solution 5 grams of crystallized 

 citric acid, and heat on the water bath for about one 

 hour. Neutralize and titrate. 



Reducing power = a. 



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