PAVY'S SOLUTION 8i 



CANE SUGAR AND MALTOSE. 



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

 this fact may be made use of in the estimation : — 



1. Add to lOO 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. 



2. Completely invert another 100 c.c. of the solution with 



hydrochloric acid ; neutralize and titrate. 



Reducing power = b ; 

 then {b-a) x 2-32 = maltose, 

 and (a - maltose x -62) = sucrose. 



GLUCOSE, CANE SUGAR, AND MALTOSE. 



1. Take 100 c.c. of the solution and titrate. The result 



includes the glucose together with maltose. 



Reducing power = a. 



2. Take another 100 c.c. of the solution, invert with citric 



acid, and then titrate. The result includes the glu- 

 cose, and the invert sugar obtained from the cane 

 sugar, together with maltose. 



Reducing power = b. 



3. Take a final lOO c.c. of the solution, and completely 



invert with hydrochloric acid. The result represents 



the whole of the sugars. 



Reducing power = c. 



Following the same reasoning as before : — 



(b-a) X -95 = cane sugar, 

 (c-b) X 2*32 = maltose, 

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



n. ESTIMATION BY MEANS OF PAVY'S SOLUTION. 



The chief disadvantage connected with the use of Fehling's 

 solution in the estimation of glucose is the difficulty in observ- 

 ing the end point of the titration owing to the red precipitate 

 of cuprous oxide ; this may be overcome by using Pavy's solu- 

 tion, which contains ammonia which dissolves the cuprous 

 oxide with the formation of a colourless solution. As before, 

 two solutions are necessary. 



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