46 PHYSIOLOGICAL CHEMISTRY. 



a drop of the dilute iodine solution and observe the production of a 

 blue color. Heat the tube and note the disappearance of the color. 

 It reappears on cooling. 



In similar tests note the influence of alcohol and of alkali upon 

 the so-called iodide of starch. 



The composition of the iodide of starch is not definitely known. 



6. Fehling's Test. On starch paste (see page 27). 



7. Hydrolysis of Starch. Place about 25 c.c. of starch paste 

 in a small beaker, add 10 drops of concentrated HC1, and boil. By 

 means of a small pipette, at the end of each minute, remove a drop 

 of the solution to the test-tablet and make the regular iodine test. 

 As the testing proceeds the blue color should gradually fade and 

 finally disappear. At this point, after cooling and neutralizing with 

 solid KOH, Fehling's test (see page 27) should give a positive result 

 due to the formation of a reducing sugar from the starch. Make 

 the phenylhydrazine test upon some of the hydrolyzed starch. What 

 sugar has been formed? 



8. Influence of Tannic Acid. Add an excess of tannic acid 

 solution to a small amount of starch paste in a test-tube. The liquid 

 will become strongly opaque and ordinarily a yellowish-white pre- 

 cipitate is produced. Compare this result with the result of the 

 similar experiment on dextrin (page 49). 



9. Diffusibility of Starch Paste. Test the diffusibility of starch 

 paste through animal membrane or parchment paper, making a 

 dialyzer like one of the models shown in pig. i, page 25. 



INULIN, (C 6 H 10 5 ) X ., 



Inulin is a polysaccharide which may be obtained as a white, 

 odorless, tasteless powder from the tubers of the artichoke, elecam- 

 pane or dahlia. It has also been prepared from the roots of chicory, 

 dandelion and burdock. It is very slightly soluble in cold water 

 and quite easily soluble in hot water. In cold alcohol of 60 per 

 cent or over it is practically insoluble. Inulin gives a negative reac- 

 tion with iodine solution. The " yellow " color reaction with iodine 

 mentioned in many books is doubtless merely the normal color of 

 the iodine solution. It is very difficult to prepare inulin which does 

 not reduce Fehling's solution slightly. This reducing power may 

 be due to an impurity. Practically all commercial preparations of 

 inulin possess considerable reducing power. 



Inulin is Isevo-rotatory and upon hydrolysis by acids or by the 



