ESTIMATION 133 



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 

 glucose, and the invert sugar obtained from the cane 

 sugar, together with maltose. 



Reducing power = b. 



3. Take a final 100 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 — 6) X 2-32 = maltose, 

 and a — (maltose X -62) = glucose. 



II. 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 : moreover, if the solution to be titrated con- 

 tains ammonium salts, the cuprous oxide will not be pre- 

 cipitated. These objections may be overcome by using 

 Pavy's solution, which contains ammonia which dissolves the 

 cuprous oxide with the formation of a colourless solution. 

 As before, two solutions are necessary. 



A. 8-316 grams of pure crystallized copper sulphate are 



carefully weighed and dissolved in I litre of distilled 

 water. 



B. 40-8 grams Rochelle salt. 

 40-8 grams caustic potash. 

 600 c.c. strong ammonia (-880). 

 Distilled water to l litre. 



In making up the mixture B great accuracy is not essential. 

 For titration 25 c.c. of A (very accurately measured) are 



