DIGESTIONS 129 



Demonstration 10. To show the test for grape sugar. 



Materials. Glucose, Fehling's or Benedict's solution, 1 test tubes, 

 Bunsen burner. 



Method. Place in a test tube a little glucose and water. Add to it 

 an equal volume of Fehling's solution. Heat the mixture to the boiling 

 point. 



If the color of the mixture becomes brick red after heating a short 

 time with Fehling's solution, chen grape sugar is present, a precipitate 

 will be formed having a red, yellow, or green color, depending upon the 

 amount of sugar present. 



Conclusion. Is Fehling's solution a test for cane sugar? Explain. 



Laboratory Exercise. Wash some dry, unsprouted corn grains and 

 test them for grape sugar. Then cut some corn grains that have just 

 begun to germinate, lengthwise, through the embryo, and test for 

 grape sugar. Look for changes in color between the embryo and 

 endosperm. 



Using a diagram, fill in with correct colors the changes that took 

 place when germinating corn was tested. 



Digestion. The change of starch to grape sugar in the corn 

 is due to a process called digestion. If you chew for a little time 

 a bit of unsweetened cracker — which we know contains starch — 

 it will begin to taste sweet, and if the chewed cracker is tested with 

 Fehling's solution, some of the starch will be found to have changed 

 to grape sugar. Here, again, the process of digestion has taken 

 place. Both in the corn and in the mouth, this change is brought 

 about by the action of chemical substances known as digestive 

 ferments, or enzymes (en'zlmz). Such substances have the power 



1 Fehling's solution may be made as follows : Add 35 g. of copper sulphate to 

 500 cc. of water. Solution No. 1. 



To 160 g. caustic soda (sodium hydroxide) and 173 g. Rochelle salt, add 500 cc. 

 of water. Solution No. 2. 



For use mix equal parts of solutions 1 and 2. This may also be obtained from 

 druggists, in tablets. 



Benedict's second solution. — Copper sulphate ........ 17.3 g. 



Sodium citrate 173.0 g. 



Sodium carbonate (anhydrous) . . . 100.0 g. 



Make up to 1 liter with distilled water. 



With the aid of heat dissolve the sodium salts in about 600 cc. of water. Pour 

 through filter paper into a glass graduate and make up to 850 cc. with distilled 

 water. 



Dissolve the copper sulphate in about 100 cc. of water, and make up to 150 cc. 

 with distilled water. Pour the carbonate citrate solution into a large beaker and 

 add the copper sulphate solution slowly with constant stirring. 



— After Hawke's Biochemistry. 



