THE ACTION OF AMYLASE ON STARCH 107 



with alcohol simply filtered, re-dissolved in water, re-precipi- 

 tated with alcohol, washed with alcohol and dried in vacuo. 



THE QUANTITATIVE STUDY OF THE ACTION OF AMYLASE 

 ON STARCH 



It is evident from the foregoing experiments that, to follow 

 exactly the course of the change which takes place when 

 malt extract acts upon a solution of starch, it is necessary to 

 make use of methods which will enable the change to be 

 followed when all the bodies concerned are present in solution 

 together, since to isolate any one of them will be likely to 

 decompose the others. The following properties are therefore 

 made use of in studying the reaction : 



(1) Specific gravity ; 



(2) Optical activity ; 



(3) Cupric oxide reducing power. 



(1) Specific Gravity. It is possible to determine, e.g., the 

 amount of sugar present in a solution by comparing the 

 specific gravity of the solution with that of a solution of sugar 

 of known strength. 



The specific gravity is best determined by means of the 

 specific gravity bottle. For this purpose a 50 c.c. specific 

 gravity bottle with a perforated stopper is required ; the bottle 

 must be cleaned thoroughly by washing with distilled water 

 and rinsing out with a little strong alcohol. The bottle is 

 then gently warmed over a flame and air sucked through by 

 means of a glass tube or blown through with the foot-bellows 

 until it is quite dry ; it is then allowed to cool in a desiccator 

 and accurately weighed. The bottle is now filled with 

 distilled water at a temperature of 15'5 C. (which is the 

 temperature of graduation of the bottle) by completely 

 immersing it in a beaker of distilled water which has been 



