28 EXPERIMENTAL PHYSIOLOGY 



XIV. — Carbohydrates — Starch. 



Apparatus. — Solution of iodine,i laundry starch, white of egg, 

 olive oil, test tubes. 



Directions — Place a little starch in a test tube and fill 

 the tube a quarter full of water. Shake it. Does the 

 starch dissolve? Boil; what happens to the starch? 



Put a little of the starch paste in a test tube with an 

 inch of water. Boil. Now add a drop of the solution of 

 iodine. What color does the paste become? 



Test a little white of egg and olive oil (which contain no 

 starch) in the same way. Do you get the same result? 



(This test will indicate the presence of starch, whatever 

 may be its form.) 



XV. — Carbohydrates — Grape Sugar. 



Apparatus. — Fehling's solution,2 raisins, starch, oil, test tubes. 



Directions. — Mince the raisins, cover with water in a test 

 tube, and let stand until the grape sugar (glucose or 

 dextrose) has dissolved. Put a little of the clear solu- 

 tion in a second test tube and dilute it with double its 

 volume of water. Add a few drops of Fehling's solution 

 and heat to boiling. When no further change in color 



^ To make the iodine solution, dissolve a teaspoonful of potassium iodide 

 crystals in a tumbler of water. Add crystals of iodine and stir until a rich 

 wine color is obtained. This may be bottled and used as needed. 



2 To make Fehling's solution: 



A. Dissolve 35 grams of copper sulphate in 500 c.c. of water. Label this 

 solution (A). 



B. Dissolve 160 grams of caustic soda and 173 grams of Rochelle salts in 

 500 c.c. of water. Label this solution (B). 



Keep these two solutions separate until ready for use. Prepare for test 

 by mixing equal quantities. 



