FOOD MATERIALS AND HOW TO DETECT THEM 23 



cold water and shake it vigorously. Set it aside for a day 

 and note the sediment on the bottom of the bottle. 



Pour off the water and remains of potato pulp and examine 

 the deposit on the bottom of the bottle. What is its color? 

 Take out a little and boil it in a test tube of water. How 

 does it change in color and consistence? Add a drop of 

 iodine solution. What is the result ? What is the substance 

 obtained from the potato ? 



Add a teaspoonful of water to a heaping tablespoonful 

 of flour and mix them thoroughly. When the water has 

 taken up all the flour possible, remove the dough and wash 

 it by holding it under a dripping faucet. Test the water 

 which washes the dough. What does it contain? When 

 the dough has been reduced to a grayish mass, test it for 

 protein. Burn a little. Result? 



Note. In both these exercises, the separation can be hastened 

 if the potato pulp or dough is placed in a cheesecloth bag and washed 

 in clear water. In the first case, the pulp of the potato will remain 

 in the bag while the starch will come through. In the second case, 

 the starch will come through and the gluten, a protein, will be 

 left in the bag. 



Note. Iodine solution is made by dissolving a teaspoonful 

 of potassium iodide in a tumbler of water and then adding a few 

 crystals of iodine. The solution should be of a rich wine color. 

 Bottle the solution for future use. 



10. SUGARS 



Object. To find out how to recognize (a) cane sugar 

 and (&) grape sugar (glucose) in foods. 



Apparatus. Cane sugar, glucose, raisins, figs, maple sugar, 

 hydrochloric acid, Fehling's solution or Benedict's solution, tubes, 

 lamp, etc. 



