370 PRACTICAL ORGANIC CHEMISTRY add 1-2 drops of dilute iodine solution. A deep blue colour is pro-duced which disappears on boiling and reappears on cooling. 3. Hydrolysis by adds. Place 15 ml. of starch solution in a boiling-tube, add i ml. of cone. HCl, mix well and place in a boiling water-bath for 20 minutes. Cool and add 2 drops of iodine solution to i ml. of the solution: no blue coloration is produced. On the remainder, perform tests for glucose: in particular show that glucosazone can be formed. Neutralise the excess of acid before carrying out these tests. (Note that a more concentrated acid is required to hydrolyse starch than to hydrolyse the disaccharides, such as sucrose.) 4. Microscopic appearance. Place a small amount of dry starch on a microscope slide, add a drop of water, cover with a slip and examine under the microscope. Characteristic oval grains are seen which have concentric rings round a hilum which is towards one end of the grain. Run a drop of
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