98 THE CARBOHYDRATES 



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 su^far 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 - b) x 232 = 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 ; 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. 



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



carefully weighed and dissolved in one litre of dis- 

 tilled water. 



B. 40-8 grams Rochelle salt. 

 40*8 grams caustic potash. 



600 c.c. strong ammonia (*88o). 

 Distilled water to one litre. 



