CH. XIIl] SUGARS. 277 



Soluble Carbohydrates (Dextrins, Sugars, etc.). 



These will partly be present in the cold-water extract 

 but some of the sugars will be found in the previous 

 alcohol extract as already pointed out. 



The examination of the solutions will depend on the 

 nature of the results required ; the simpler methods will 

 frequently be sufficient for problems on metabolism, but 

 methods for dealing with cases where more detailed 

 information is required are also given. 



Since the common sugars, glucoses, cane-sugar, and 

 maltose are all undoubtedly plastic substances, it is often 

 sufficient to determine these together as fermentable 

 sugars and to calculate the result as 'glucoses.' The 

 simple fermentation processes can often be used, as it is 

 but rarely that solutions are obtained (after removal of 

 tannins, etc., as above described) which contain sugars that 

 do not ferment on the addition of yeast. 



Dextrins do not ferment, or hinder fermentation, and it 

 is not therefore necessary to separate them from a solution 

 in using the fermentation methods. 



Dextrins interfere much with determinations of sugars 

 by the volumetric ' reducing ' processes (in many cases they 

 act as reducing agents), and although the precipitation 

 by alcohol is tedious and troublesome it is generally better 

 to use it, and to make the estimations with solutions free 

 from dextrins. 



A full discussion of the methods for estimating sugars 

 in mixtures of glucoses, cane-sugar, and maltose need not 

 be entered into here, but it may be stated that the process 



