CARBOHYDRATES 261 



Lactose. Perform the following tests : 



29. Solubility in water, alcohol and ether. 



30. Benedict's. 



31. Phenylhydrazine. 



32. Fermentation. 



This test is of importance in identifying lactose. In testing 

 for lactose a control should be run with a lactose solution, to 

 make sure that no lactose splitting enzyme is present in the yeast 

 used. 



Lactose may also be distinguished from all other reducing 

 sugars except galactose by the mucic acid test. Lactose may be 

 distinguished from galactose by the fermentation test. 



III. Polysaccharides 

 Starches. 



33. Potato Starch. Pare a small potato and with a pocket 

 knife scrape it to a fine pulp. Mix with 300-400 c.c. of distilled 

 water and whip up thoroughly. Strain through a piece of cheese 

 cloth to remove the coarse particles. The starch granules will 

 settle rapidly to the bottom of the beaker. Wash once or twice 

 by decantation and examine under a microscope. Draw the gran- 

 ules. Filter off a portion and allow it to dry in the air. Make 

 the following tests on starch. 



34. Solubility. Refer to directions for determining solubility 

 as given under Dextrose. In the case of starch, the substance is 

 tested for in the filtrate by chemical means. Test the solubility 

 of starch in cold water, hot water, alcohol, and ether. If un- 

 certain of the result, filter and test the filtrate for starch by the 

 iodine test as described below. 



35. Preparation of Starch Solution. Heat about 75 c.c. of dis- 

 tilled water to boiling. To this add about % gram of starch 

 which has been rubbed to a thin paste with a small amount of 

 cold water. Boil very slowly for about 15 minutes, replacing 

 water lost by evaporation. Use the resulting opalescent solution 

 for the following tests. 



