xiv GENERAL INTRODUCTION 



or dark blue ; if little starch, pale blue ; if no starch, brown 

 or yellowish. 



Make pastes with wheat flour, potato starch, and corn 

 starch. Treat a little of each with a solution of rather 

 dilute tincture of iodine. Try grains from crushed rice 

 with the same solution. Are they the same color? Cut a 

 thin section from a potato, treat with iodine and examine 

 under the microscope. 



To study Starch Grains. Mount in cold water a few 

 grains of starch from each of the following : potato, wheat, 

 arrowroot (buy at drug store), rice, oats, corn. Study under 

 microscope the sizes, forms, layers, fissures, and location 

 of nuclei, and make a drawing of a few grains of each. 



Test for Grape Sugar. Make a thick section of a bit of 

 the edible part of a pear and place it in a bath of Fehling's 

 solution. After a few moments boil the liquid containing 

 the section for one or two minutes. It will turn to an 

 orange color, showing a deposit of an oxid of copper and 

 perhaps a little copper in the metallic form. A thin sec- 

 tion treated in like manner may be examined under the 

 microscope, and the fine particles, precipitated from the 

 sugar of the pear, may be clearly seen. (Fehlings solution 

 is made by taking one part each of these three solutions 

 and two parts of water: (i) Copper sulfate, 9 grams in 

 250 cubic centimeters of water; (2) sodium hydroxid, 30 

 grams in 250 c.c. water ; (3) Rochelle salts, 43 grams in 

 250 c.c. water.) 



Test for Nitrogenous Substances, or Proteids. - - Put a little 

 white of egg into a test tube and heat slowly. What change 

 takes place in the egg? Put another part of the white of 

 egg into a test tube and add dilute nitric acid. Compare 

 the results of the two experiments. White of egg is an ex- 

 ample of a proteid ; that is, it is the form of nitrogen most 



