PRACTICAL WORK 47 



glass and add a drop of very dilute iodine. Shake the tube 

 vigorously again at intervals and after another two minutes 

 pour a little into a third watchglass, adding a drop of very dilute 

 iodine. Note the colours in the three cases. The pinkish colour 

 with iodine is due to the formation of dextrin, a carbohydrate 

 intermediate between starch and sugar. On adding a few drops 

 of Fehling's solution to the contents of the test tube after half 

 an hour, and heating, a slight reducing effect should be obtained. 

 This is due to the glucose present. 



(4) Test with iodine solution a piece of good writing paper 

 (nearly pure cellulose) across which strong sulphuric acid has 

 been streaked. 



(5) Examine the demonstration specimen of paper boiled in 

 strong sulphuric acid, neutralized with alkali and then treated with 

 Fehling's solution to demonstrate the formation of a reducing 

 sugar (glucose) ; also of the cut date stones (the very thick 

 walls of whose cells consist of cellulose) similarly treated. 



(6) Note that desiccated coconut " meat " (food material 

 used by the embryo growing into a seedling) is oily to the touch. 

 Place some in a test tube with water and boil : the oil rises to 

 the surface. Add a few drops of Sudan 3 (an aniline dye) and 

 allow to stand : the oil is coloured red. Add a few drops of 

 Sudan 3 to olive oil in a test tube : the oil is coloured red. Pour 

 half the red oil into another test tube. Add a little alcohol to 

 one and a little water to the other. Note the position taken up 

 by the water and alcohol respectively in relation to the oil : 

 also the coloration resulting. 



(7) The two substances provided in separate test tubes are 



(a) white of egg shaken up with water, which is a typical protein, 



(b) bean meal shaken up with salt solution. Divide each into 

 three portions and subject each set of three to the following 

 tests, noting the coloration in each case : 



(i) Add a few drops of strong nitric acid. Boil and then 

 cool thoroughly. Add a few drops of ammonia solution) xantho- 

 proteic reaction). 



(ii) Add one drop of dilute copper sulphate solution. Now 

 add excess of caustic soda or potash (biuret reaction). 



(iii) Add a few drops of iodine solution. 



