56 CELL-CONTENTS AND CELL-WALLS. 



so that the water boils gently for about a minute, then 

 cover (adding a drop of water if necessary) and examine ; 

 if grape sugar is present, the granular red precipitate of 

 cuprous oxide will be seen in the cells. To test sections 

 for cane sugar, boil them in 10 per cent, sulphuric acid in 

 a test-tube, then test as before with Fehling ; or place the 

 Fehling at once on the sections, add a few drops of the 

 acid, and boil gently on the slide. 



(a) Squeeze the juice of some grapes into a test-tube, 

 add Fehling, boil, and note the precipitate formed. 



(b) Cut sections of a ripe Q-rape ; mount in water, cover, 

 and note the transparent colourless thin-walled cells with 

 large vacuole and scanty protoplasm. (1) Place some 

 sections in strong alcohol in a watch-glass for a few 

 minutes ; mount in alcohol, cover, and note the numerous 

 sugar crystals in the cells. Irrigate with water; the 

 crystals are dissolved. (2) Test sections for grape sugar 

 with Fehling' s solution. 



Make similar experiments with pear, apple, and other 

 fruits. 



(c) Mince up some Beet-root, boil in water, pour the red 

 juice into two test-tubes. To one add Fehling and boil 

 no precipitate ; to the other add acid, boil, add Fehling, 

 boil again precipitate formed. 



(d) Cut sections of Beet-root ; the cells are transparent, 

 with scanty protoplasm, the sugar-containing sap is col- 

 oured. (1) Place some of the sections in alcohol for a 

 few minutes, mount in alcohol, and note the sugar crystals 

 smaller than those seen in the cells of the Grape. 

 (2) Test other sections for grape-sugar with Fehling (no 

 result), and for cane sugar by boiling with acid and then 

 adding Fehling (precipitate formed). 



67. Experiments with Solid Starch. For experiments 

 with starch use ordinary laundry starch or (better) the starch 

 powder sold by chemists. 



Heat some dry starch in a test-tube. Note the condensation of 

 water in the upper part of the tube. This proves the presence of 

 hydrogen and oxygen in starch (since water is composed of these 



