THE DETERMINATION OF REDUCING SUGARS. 



Reduction Process employing Prolonged Heating. 



There are not wanting objections to a boiling of the copper and glucose 

 solutions for a short period, and processes involving the keeping of the materials 

 for up to 15 minutes on a water bath have been proposed. These processes 

 have never been so generally adopted as have those entailing a boiling of short 

 period, and Munson and Walker 7 in particular have shown that serious error 

 due to surface oxidation is thereby introduced. 



Dextrose Ratio of Reducing Sugars. The tables of Allihn 

 give the equivalence between copper and dextrose ; the methods described and 

 the tables are equally applicable to all reducing sugars, as Browne 8 has shown 

 that the relative reducing powers of the different reducing sugars are constant. 

 The dextrose ratio of levulose is given by Browne as '915, i.e., where a certain 

 weight of dextrose reduces one part of copper, the same weight of levulose 

 will reduce '915 part of copper, hence if levulose is being determined, the 

 analysis is made exactly as if for dextrose, the final result being divided by 

 915, so as to correct for the difference in the reducing powers of the sugars. 



The reducing powers of some sugars compared with dextrose as unity are 



Dextrose .. .. .. .; . .. .. I'OOO 



Levulose . . . . . . . . . . . . .... '915 



Xylose.. ., .. _.. ... -983 



Arabinose .. ., .. .... 1.032 



Invert Sugar . . . . . . . . . . . . . . -957 



Galactose .. .. .. .. ..... .... '898 



Lactose -678 



Maltose .. .. ... - .. .. .. -620 



The Effect of Cane Sugar in the Determination of 

 Reducing Sugars. Cane sugar has a slight reducing action on the copper 

 solution, and this action is proportional to the amount of cane sugar present, 

 and to the amount of copper left unreduced ; the error becomes very notice- 

 able when bodies such as raw cane sugars containing 96 per cent, cane sugar 

 and less than 1 per cent, reducing sugars are being analysed. This error is 

 thus corrected by Browne. 8 



" The grms. of sucrose in the 25 c.c. of solution to be analysed by Allihn's 

 method are divided by the mgrms. of dextrose found-f 40 ; the quotient will 

 give the required correction in grms. to be deducted." 



For the determination of invert sugar in the presence of cane sugar the 

 methods of the Association of Official Agricultural Chemists, which are based 

 on those of Herzfeld and of Meissl and Hiller, enjoin the use of a copper 

 solution different from that of Allihn ; for the determination of dextrose alone 

 Allihn's copper solution is used; as the use of two solutions is inconvenient, 

 the writer only gives the method of Browne for the correction due to the 

 presence of cane sugar. 



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