96 THE USES OF FOODS 



be made on cold starch, but is quicker and surer if the substance tested 

 has been heated to the boiling point. The heat causes the granules 

 to swell and burst the cell walls which inclosed them. 



Test for Grape Sugar: Place a little grape sugar in a test tube one fourth 

 full of water. Add an equal amount of Fehling's solution. Heat to 

 the boiling point. The characteristic brick red color which appears 

 is the test for grape sugar. Cane sugar heated or digested with diluted 

 acid changes in part to grape sugar, but pure cane sugar will give no 

 result with this test. 



Test many foods, as oatmeal, bread, potatoes, rice, sirup, molasses, 

 cabbage, apples, bananas, candy, cheese, meat, etc., for starch and 

 sugar. List the foods under the following headings : 



Experiment. To test for fats or oils. 



Materials : Pork or butter, oily nut, corn meal, paper. 



Method and Results : Rub a piece of pork or butter on a piece of paper. 

 Lay a crushed nut or a little corn meal on a piece of paper and place 

 it in a warm oven for a few minutes. The oil or fat absorbed by the 

 paper makes a semi-transparent spot which is seen when held toward 

 the light. 



Application: Test various foods. Those which give a test without 

 warming in the oven have a higher per cent of fat. 



Experiment. To test for protein. 



Materials: White of egg (a typical protein). Test tube. Concentrated 

 nitric acid. Ammonia. 



Method and Results: Pour the white of egg into boiling water to coagu- 

 late it. Pour off the water and add a few drops of strong nitric acid 

 to the solid white of egg. Is there any change? Rinse the acid off 

 with water and add ammonia. The lemon color after the addition of 

 the acid and the deep orange following the addition of the ammonia 

 complete the test for protein. Heat quickens the reaction. 



Application of Test: Try this test on such foods as lean meat, bread, 

 cheese, beans, and rice. Which ones show the presence of protein? 



