24 



Carbohydrates are classified asMonosaccharids or g-lucoses, 

 (simple sugars) ; disaccharids or saccharoses ; polysaccharids 

 or amyloses. 



The monosaccharids (CgHjjOg) include dextrose (glucose 

 or grape sugar), galactose, levulose, glycuronic acid. They 

 cannot be broken down into simpler sugars. 



The disaccharids (Ci2H220ji) on taking%p one molecule of 

 water split and yield two simple sugars. Examples are sac- 

 charose (cane sugar), maltose (malt sugar), lactose (milk 

 sugar). 



The polysaccharids (C|,H,„05)n do not resemble sugars. 

 They have no sweet taste, and form simple sugars only after 

 several reactions. Examples are starch, dextrin, animal gum, 

 glycogen, and cellulose. 



45. Starch (CgHjjOJn 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. 



46. Squeeze some dry starch powder between the thumb 

 and forefinger, and note the peculiar crepitation sound and 

 feeling. 



47. Place 1 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 heat for ten minutes 

 over boiling water. Does the starch go into solution? Filter 

 and test with a drop or two of the iodine solution. 



48. Add powflered dry stafch 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 1 

 gram of iodine and shake until dissolved.) 



49. 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 may occur when cooled. 



50. Render some of the starch mixture alkaline by 

 adding, slight excess of caustic potash. Add iodine solution. 

 What is the result ? 



