THE ACTION OF AMYLASE ON STARCH 103 



The action of malt extract upon starch may now be studied 

 as follows : A 3 per cent, solution of starch paste (i.e., 

 six grams of starch to 200 c.c. of water) is first prepared. In 

 preparing starch paste the starch should first be rubbed 

 down in a mortar to a thin cream with a portion of the water 

 used, while the remaining volume of water is heated to boiling ; 

 the starch cream is then carefully added, stirring the while. A 

 solution of soluble starch prepared as above contains no 

 visible undissolved particles. 



With the extract of malt and the cold starch solution it is 

 now possible qualitatively to examine the changes which 

 occur when the two are brought together. For this purpose, 

 say, six small beakers or large test-tubes may be used and 

 about 10 c.c. of starch solution placed in eauh, together 

 with -J- c.c. of the filtered malt extract. The test-tubes are 

 then placed in a constant-temperature water-bath at a tem- 

 perature of 60 C. The test-tubes can now be observed from 

 time to time. The first change to be noted is the clarification 

 of the starch ; simultaneously with this it may be found that 

 the ordinary blue colour is no longer given when a drop of 

 dilute iodine solution is added to the solution. On removing 

 the second test-tube after the lapse of a further period, the 

 colour of the iodine will be found to have become distinctly red. 

 If simultaneous tests are made by the addition of Fehling 

 solution, a gradually increasing amount of precipitation will 

 be noted until finally no reaction is given by the iodine, while 

 a copious red precipitate is formed on boiling with the Fehling 

 solution. 



This experiment indicates that the action of the malt 

 extract upon the starch solution is progressive. In the first 

 place a substance is formed which gives a purple colour with 

 iodine but does not reduce Fehling solution. Later on sub- 

 stances are formed which give a red coloration with iodine, 

 and eventually only the sugar or Fehling reducing substance 

 can be detected. A more exact investigation of the first 



