FOOD .-- 215 



small starch granules will be seen. Each granule shows concentric 

 markings. Add iodine solution ; the granules turn blue or blue black. 

 Examine other kinds of starch granules, of corn, oats, rice, etc. 



96. Test for Sugar. To one fourth test tube of a weak solution 

 of glucose, add an equal amount of a 15 per cent solution of caustic 

 soda. Shake, and after adding a few drops of a 1 per cent solution 

 of copper sulphate, boil for a few minutes. The liquid changes 

 from blue to yellow, or, if much sugar is present, to brown in color, 

 and a precipitate is formed. To show that the change in color is due 

 to the sugar present, repeat the preceding, using pure water, or any 

 solution known not to contain sugar, instead of the sugar solution. 

 This test is known as Trommer's test. It is not a test for cane sugar, 

 nor does it distinguish between glucose, malt sugar, and milk sugar. 



97. Fats. Put some melted butter, or olive oil, into a test tube 

 one fourth full of water. The fat rises to the top. Shake well ; a 

 whitish mixture, or emulsion, is the result, but the oil and water 

 quickly separate. To the contents of the test tube, add an equal 

 amount of 1 per cent solution of carbonate of soda (an alkali), and 

 shake. The emulsion with the alkali lasts much longer than that 

 with water alone. Add a drop or two of oleic acid (a fatty acid) to 

 the mixture, and shake well; the emulsion lasts longer than before. 

 It will be learned later that the fats are only slightly dissolved in 

 digestion, but are chiefly emulsified. 



98. Examine with the microscope some of the emulsion prepared 

 above. The fat will be found to be broken up into innumerable fine 

 particles. 



99. Shake some olive oil with dilute white of egg in a test tube ; an 

 emulsion results. 



100. To one fourth test tube of water, add a few drops of oleic 

 acid, and shake. The oil rises to the surface as in the preceding- 

 experiments. To the contents of the test tube add carbonate of soda 

 as before. A white precipitate of soap is formed. An alkali and a 

 fatty acid form soap. 



During digestion some of the fat is broken down into glycerin and 

 fatty acids. The latter unite with alkalis in the intestine to form sol- 

 uble soap. 



101. Flour. Boil a little flour in water and test with iodine for 

 starch. 



102. Place a little flour in from five to ten times its bulk of water 



