292 STARCH AND [CH. XIV 



Quantitative. 



A measured quantity of acid solution (containing 1 p.c. 

 sulphuric acid) is placed in a strong glass tube and the 

 open end carefully sealed. The tube is then heated 

 and kept at 120 C. for half-an-hour. When cool the 

 tube is carefully opened, the contents washed out and 

 made up to a known volume with distilled water, and the 

 glucose estimated, after neutralising, by one of the volu- 

 metric processes. 



Glucose found x '9 = starch (anhydrous), (C G H 10 5 ). 



If diastase (malt-extract) instead of dilute acid is used 

 to extract the starch from the material, the solution 

 obtained (containing dextrins and maltose) may be treated 

 in the same way to convert all the first products of the 

 hydrolysis of the starch into glucose. 



In a measured quantity of the solution, to which 

 sufficient sulphuric acid has been added to make 1 p.c. 

 acid, the glucose is estimated after heating in a sealed 

 tube at 120 C. for half-an-hour. 



When this method is used a correction has to be made 

 for the reducing power of the substances produced by the 

 action of the acid at 120 C. on the malt extract. 



For this purpose a quantity of the malt extract equal 

 to that taken for dissolving out the starch from the 

 original material must be treated as directed above, and 

 the glucose produced in the operation determined. 



The amount of glucose found in this last experiment 

 must be subtracted from the total amount found in the 

 actual experiment, as the difference between these amounts 



