488 APPENDIX 



starch from sticking to the inside of the tube. Note that the 

 starch swells up and forms a paste, but does not actually dissolve. 

 Cool the paste by holding the test tube in cold water. When 

 sufficiently cool add a drop or two of iodine and note that the 

 starch turns blue. This change of color serves as a test for 

 starch whether uncooked or cooked. Hence we see that undi- 

 gested starch is in the form of granules which do not dissolve 

 in water, but which turn blue when treated with iodine. 



(2) The chemical test for digested starch, i.e., grape sugar 



Into a test tube about one fourth full of water put a pinch of 

 grape sugar, shake the tube, and npte that the grape sugar dis- 

 solves. Test the solution with iodine and note that the blue 

 color does not appear. 



Prepare another solution and to it add about one fifth its 

 volume of a strong solution of sodium hydrate, then to this 

 mixture add a drop or so of a one-per-cent solution of cupric 

 sulphate. Shake the tube to mix the contents thoroughly. 

 Note the light blue color. Boil the contents of the tube and 

 the color changes, varying from lignt yellow to orange or brick 

 red. Hence it is seen that digested starch (grape sugar) dis- 

 solves in water, does not turn blue with iodine, but turns yellow 

 or reddish when boiled with a mixture of sodium hydrate and 

 cupric sulphate. 



(3) The digestion of starch by saliva 



Collect about a third of a test tube full of saliva, the flow of 

 which may be promoted by chewing a piece of rubber or a 

 button. Dip a piece of red litmus paper into the saliva and 

 note that the paper becomes faintly blue, indicating that the 

 saliva is slightly alkaline in its chemical reaction. In another 

 test tube make a mixture of about equal parts of saliva and 

 water, and to this add a few drops of cool starch paste. Hold 

 the tube containing this mixture in the hand for five, or ten 

 minutes in order to keep it at the temperature of the body. 

 After a few minutes pour a portion of the mixture in another 

 tube and test with iodine, which will probably give the blue 



