LIVING PAETS OP THE STEM 117 



orange color and throwing down an orange or reddish 

 deposit, when they are added to a brilliant blue alkaline 

 solution of copper, known as FehUng^s solution?- The 

 color or deposit will not appear until the solution has 

 been heated to boiling. 



EXPERIMENT XXIV 



Testing for Grape Sugar. — Heat to boiling in a test-tube or a 

 small beaker some weak syrup of grape sugar or some honey, much 

 diluted with water. Add Fehling's solution, a few drops at a time, 

 until a decided orange color appears. Repeat the test with the 

 water in which some slices of onion have been boiled, filtering the 

 water through a paper filter and heating again to boiling before 

 adding the test solution.* 



127. Proteids in the Onion. — Since the onion grows 

 so rapidly on being planted in the spring, there must be 

 a large supply of food in the bulb ; there may be other 

 substances present besides sugar. 



EXPERIMENT XXV 



Testing an Onion for Other Stored Food. — Test a rather thick 

 slice of onion by heating it in a porcelain evaporating dish with a 

 little strong nitric acid until the latter begins to boil and the onion 

 becomes somewhat softened.* Rinse off the slice of onion in a stream 

 of water, then pour on it a few drops of ammonium hydrate and 

 observe any change of color. What is proved ? See Sect. 29. 



128. Tabular Review of Experiments. 

 [Continue the table from Sect. 74.] 



1 For the preparation of the solution see Handbook. 



2 The deposit will in this case, even if orange at first, finally become black, 

 probably owing to the presence of sulphur in the onion. 



i Do not allow the acid to touch the clothing, the hands, or any metallic 

 object. 



