25 



51. Acidify with dilute sulphuric acid, then add iodine. 

 What is the result ? 



52. Add some solution of tannic acid. Note result and 

 then heat. 



53. Place some strong- starch mixture in a dialyzer and 

 the latter in distilled water. Allow it to stand for some time 

 and test the water for starch. 



54. Saturate a portion of the starch mixture with crystals 

 of ammonium or magnesium sulphate. Filter. Dilute the 

 filtrate with an equal volume of water and add a drop or two 

 of the iodine solution. Is the starch precipitated by the salt ? 



55. Glycogen (C|.Hj„05)n is a polysaccharid found exclu- 

 sively in animals chiefly in the liver, in the leucocytes, in all 

 embryonic tissues, and in muscle. It is also known as animal 

 starch. It forms an opalescent solution in water, gives a red 

 color with iodine. On boiling with acids it is converted into 

 dextrin, then maltose and dextrose. The amylolytic enzymes, 

 by hydrolysis, produce the same chang-es. Basic lead acetate 

 precipitates glycogen. Barfoed's reagent is not reduced. 



56. Dextrin. (CgHiijOs) is an intermediate product in the 

 hydration of starch. ^ 



57. .-Dissolve some dextrin, about 2%, in boiling water 

 (100 cc.) and cool. Add iodine solution — a reddish brown 

 color, which disappears on heating and returns on cooling. 

 (The sti^ent should take two test tubes placing the dextrin 

 solution in one, and an equal volume of water in the other. 

 Add to both an equal volume of iodine solution and thus com- 

 pare the difference in color.) Dextrin is made commercially 

 by heating starch to 200° C. 



58. Saturate a solution of dextrin (57) with ammonium 

 sulphate. Note result. Filter. Dilute with an equal volume 

 of water and test the filtrate for dextrin. 



59. Test a solution of dextrin (57) with Barfoed's rea- 

 gent and heat. Barfoed's reagent^ made by dissolving 13 

 grams of cupric acetfeate in JOOLc^ ^Milled water and add 5 cc. 

 commercial acetic acid (38% )T 



60. Test a solution of dextrin (57) with a few drops of a 

 solution of basic lead acetate. Is there a precipitate ? (The 

 lead acetate must be basic. To insure this the solution of lead 



t / 



