24 THE NATURE AND NEEDS OF LIVING MATTER 



a. Starch 



Materials. Corn starch, iodine solution, and test tube. 



Method. Crush the starch, and add a third of a test tube 

 of water to a bit as large as a pea. Add a few drops of iodine 

 solution. 1 



Observation. What change in color do you note ? Note. 

 If a large amount of starch is present, the material will turn 

 black ; if a smaller amount, it will turn a deep blue. 



b. Grape Sugar 



Materials. Glucose or grape sugar, 2 Fehling's solution or 

 preferably 3 Benedict's second solution, test tubes, and alcohol 

 lamp or Burisen burner. 



Method a. Dissolve some glucose in water in a test tube. 

 Add a few drops of Fehling's solution and boil. 



Observation. What change in color do you observe ? Note. 

 If grape sugar is present in any substance, the contents of the 

 tube will change to a yellowish, deep orange, or brick-red color. 



1 Iodine solution may be made by adding a few crystals of iodine to enough 

 95 per cent alcohol to dissolve it well. Or to 1 gram of iodine crystals, add 

 | gram of potassium iodide, and dilute to a dark brown color in 30 per cent 

 alcohol. 



2 Fehling's solution may be made as follows : Add 35 g. of copper sul- 

 phate to 500 cc. of water. Solution No. 1. 



To 160 g. caustic soda (sodium hydroxide), and 173 g. Kochelle salt, add 

 500 cc. of water. Solution No. 2. 



For use mix equal parts of solutions 1 and 2. This may also be obtained 

 of druggists, in tablet shape, or address Jno. Wyeth and Bros., Phila- 

 delphia. 



3 Benedict's second solution. Copper sulphate 17.3 grams. 



Sodium citrate 173.0 grams. 



Sodium carbonate (anhydrous) 100.0 grams. 

 Make up to 1 liter with distilled water. 



With the aid of heat dissolve the sodium salts in about 600 cc. of water. 

 Pour through filter paper into a glass graduate and make up to 850 cc. with 

 distilled water. 



Dissolve the copper sulphate in about 100 cc. of water, and make up to 

 150 cc. with distilled water. Pour the carbonate citrate solution into a large 

 beaker and add the copper sulphate solution slowly with constant stirring. 



