THE ACTION OF AMYLASE ON STARCH 111 



Further, if the weight of original substance present, e.g., 

 starch, is known, and the specific rotatory power of dextrin 

 and maltose respectively, then the amount of conversion which 

 has taken place after the first appearance of dextrin can be 

 determined by an observation of the specific rotatory power 

 of the mixture, e.g., the specific rotatory power of dextrin is 

 195, of maltose 135 '4. If the specific rotatory power of the 

 mixture is, say 165'2, the relative proportions present can 

 be calculated from the following equation : — 



195a; + 135-4 (I -x)= 165-2 



X in this case will be found to equal 0-5, i.e., the dextrin and 

 maltose were present in equal quantities. 



(3) Cupric Oxide reducing Power.— The cupric oxide re- 

 ducing power of sugars is conveniently referred to a typical 

 sugar taken as a standard. This standard is generally known 

 as K, the amount of CuO reduced by one gram of glucose 

 being taken as 100. 



The actual amount of CuO reduced from Fehling solution 

 by one gram of glucose is 2-205 grams ; the sugar reducing say 

 1-345 grams CuO per gram would give the value for K as 

 61, thus : — 



2-205 : 1-345 :: 100 : 61 



In the case of starch it is usual to take maltose as a 

 standard, in which case the letter E is used instead of K ; thus 

 a substance with three-quarters the reducing power of maltose 

 would be considered to have a reducing power E^g instead of 

 K46.76. A rapid method for determining cupric oxide reducing 

 power is given in the following paragraphs, based on the 

 Eeport of the Malt Analysis Committee to the Council of the 

 Institute of Brewing. 



The method is there used for determining the diastatic 

 activity of malt. It may be used generally for determining 



