OCCURRENCE OF CARBOHYDRATES IN PLANTS 49 



If the Fehling's solution is not freshly prepared, 

 it should be tested, before using, by heating a por- 

 tion in a test-tube until it boils. If a precipitate 

 of red copper oxide does not form the solution is 

 good. It is better to make this test even with fresh 

 solution. 



4. Place a very small amount of grape sugar into a test- 

 tube one-third full of water. 



5. Shake the solution and gently warm it, then add a 

 few drops of Fehling's solution. 



6. Describe what results. The effect is due to the 

 grape sugar reducing (i.e., taking oxygen from) the 

 cupric sulphate in Fehling's solution, forming 

 cuprous oxide 



7. State the test for grape sugar. 



Experiment 23. To demonstrate a test for the pres- 

 ence of cane sugar. 



8. Proceed as in the preceding experiment, using cane 

 sugar instead of grape sugar. Observe and describe 

 the result. 



9. Prepare a second test-tube with a solution of cane 

 sugar. 



10. Add several drops of hydrochloric acid, and boil the 

 mixture. 



11. Now add several drops of Fehling's solution (enough 

 to neutralize the acid). 



12. State the test for cane sugar. 



Experiment 24. To demonstrate the occurrence of 

 sugar in plant tissues. 



13. Test portions of onion, beet, sweet corn, sweet 

 potato, etc., for sugar. Describe the result in each 

 case. 



14. Write a brief summary of what you have learned 



