21 



white precipitate indicates the combination of the chloride 

 with the silver to form silver chloride. 



87. Digestive action on starch. Prepare a mixture by 

 placing I gram of starch in a mortar and adding a few cc. 

 of cold water, and mix well with the starch. Add 200 cc. 

 of boiling water, stirring all the while. Boil the fluid for a 

 few minutes. This gives a 0.5% mixture. 



88. Dilute the .saliva with an equal volume of distilled 

 water. Label four test tubes, A, B, C, and D. Into A 

 place some .saliva, boil it and add some starch mucilage. In 

 B and C place starch mucilage and saliva, to B add a few 

 drops of hydrochloric acid and to C some caustic potash. 

 To D add merely the saliva to the starch mixture. 



Place all four in a water bath not exceeding 40° C, and 

 after a time test a small portion of them for .sugar with 

 Fehling's .solution. Reserve a small amount of D. Why is 

 no sugar formed in A? In B and C a strong acid and alkali 

 arrest the action of ptyalin. Neutralize a portion of B and 

 C and test again. Is there any result? In D the starch 

 has been converted by the ptyalin into a reducing sugar. 



89. Test a portion of D with iodine solution. The ab- 

 sence of any blue color indicates that the starch has disap- 

 peared, having been converted into a reducing sugar — mal- 

 tose. Also test the remainder of A, B and C with the 

 iodine .solution. 



90. Test another portion of D withphenyl-hydraziu, (53) 

 crystals of phenyl-maltosazone should develop. Examine 

 under the microscope. 



91. Bread. Crumble up a small piece of bread in a test- 

 tube and add some cold distilled water until it softens and 

 with slight shaking disintegrates. Divide the mixture into 

 two portions. 



92. Apply a drop of iodine solution : blue color indicates 

 starch. 



93. Apply the xanthoproteic reaction to the other portion. 



