14 



(This proportion is also obtained in other substances not be- 

 longing to the carbohydrate group). 



Carbohydrates are indifferent bodies with a neutral reac- 

 tion and form only loose combinations with other bodies, 

 especiall}' with bases. 



34. Starch (CeHnjOs) n is one of the most widely dis- 

 tributed substances in plants, and it may occur in all the 

 organs of plants, either (a) as a direct or indirect product of 

 the assimilation of COj in the leaves of the plant, or (b) as 

 reserve material in the roots, seeds or shoots for the later 

 periods of generation or vegetation. 



35. Squeeze some dry starch powder between the thumb 

 and forefinger, and note the peculiar crepitation sound and 

 feeling. 



36. Place I gram of starch in a mortar, rub it up with a 

 little cold water, and then add 50 cc. of boiling water. 

 Transfer to an evaporating dish and boil over a water bath. 

 Does the starch go into solution ? 



37. Add powdered dry starch to cold water. Is it insol- 

 uble ? Filter and test the filtrate with a solution of iodine. 

 A blue color denotes the presence of iodide of starch. 



(Prepare the iodine solution as follows : Dissolve 2 grams 

 of potassium iodide in 100 cc. of distilled water, add i gram 

 of iodine and shake until dissolved). 



38. To some of the boiled portion of starch, add solution 

 of iodine. Heat and note any change that occurs. If not 

 boiled too long another change maj' occur when cooled. 



39. Render some of the starch mixture alkaline by adding- 

 caustic potash. Add iodine solution. What is the result ? 



40. Acidify with dilute sulphuric acid, then add iodine. 

 What is the result? 



41. Add some solution of tannic acid. Note result and 

 then heat. 



42. Place some strong starch solution in a parchment tube 

 and the latter in distilled water. Allow it to stand for some 

 time and test the water for starch. 



