Experiment 32. To a small quantity of this solution in a test tube add strong nitric acid, and boil. Note the formation of a white precipitate, which turns yellow. After cooling, add ammonia, and note that the precipitate becomes orange.
Experiment 33. Add to the solution of egg-albumen, excess of strong solution of caustic soda (or potash), and then a drop or two of very dilute solution (one per cent) of copper sulphate. A violet color is obtained which deepens on boiling.
Experiment 34. Boil a small portion of the albumen solution in a test tube, adding drop by drop dilute acetic acid (two per cent) until a flaky coagulum of insoluble albumen separates.
Experiment 35. Wash a potato and peel it. Grate it on a nutmeg grater into a tall cylindrical glass full of water. Allow the suspended particles to subside, and after a time note the deposit. The lowest layer consists of a white powder, or starch, and above it lie coarser fragments of cellulose and other matters.
Experiment 36. Examine under the microscope a bit of the above white deposit. Note that each starch granule shows an eccentric hilum with concentric markings. Add a few drops of very dilute solution of iodine. Each granule becomes blue, while the markings become more distinct.
Experiment 37. Examine a few of the many varieties of other kinds of starch granules, as in rice, arrowroot, etc. Press some dry starch powder between the thumb and forefinger, and note the peculiar crepitation.
Experiment 38. Rub a few bits of starch in a little cold water. Put a little of the mixture in a large test tube, and then fill with boiling water. Boil until an imperfect opalescent solution is obtained.
Experiment 39. Add powdered dry starch to cold water. It is insoluble. Filter and test the filtrate with iodine. It gives no blue color.
Experiment 40. Boil a little starch with water; if there is enough starch it sets on cooling and a paste results.
Experiment 41. Moisten some flour with water until it forms a tough, tenacious dough; tie it in a piece of cotton cloth, and knead it in a vessel containing water until all the starch is separated. There remains on the cloth a grayish white, sticky, elastic "gluten," made up of albumen, some of the ash, and fats. Draw out some of the gluten into threads, and observe its tenacious character.