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.

Experiment 42.  Shake up a little flour with ether in a test tube, with a tight-fitting cork.  Allow the mixture to stand for an hour, shaking it from time to time.  Filter off the ether, and place some of it on a perfectly clean watch glass.  Allow the ether to evaporate, when a greasy stain will be left, thus showing the presence of fats in the flour.

Experiment 43.  Secure a specimen of the various kinds of flour, and meal, peas, beans, rice, tapioca, potato, etc.  Boil a small quantity of each in a test tube for some minutes.  Put a bit of each thus cooked on a white plate, and pour on it two or three drops of the tincture of iodine.  Note the various changes of color,—­blue, greenish, orange, or yellowish.

Experiments with Milk.

Experiment 44.  Use fresh cow’s milk.  Examine the naked-eye character of the milk.  Test its reaction with litmus paper.  It is usually neutral or slightly alkaline.

Experiment 45.  Examine with the microscope a drop of milk, noting numerous small, highly refractive oil globules floating in a fluid.

Experiment 46.  Dilute one ounce of milk with ten times its volume of water.  Add cautiously dilute acetic acid until there is a copious, granular-looking precipitate of the chief proteid of milk (caseinogen), formerly regarded as a derived albumen.  This action is hastened by heating.

Experiment 47.  Saturate milk with Epsom salts, or common salt.  The proteid and fat separate, rise to the surface, and leave a clear fluid beneath.

Experiment 48.  Place some milk in a basin; heat it to about 100 degrees F., and add a few drops of acetic acid.  The mass curdles and separates into a solid curd (proteid and fat) and a clear fluid (the whey), which contains the lactose.

Experiment 49.  Take one or two teaspoonfuls of fresh milk in a test tube; heat it, and add a small quantity of extract of rennet.  Note that the whole mass curdles in a few minutes, so that the tube can be inverted without the curd falling out.  Soon the curd shrinks, and squeezes out a clear, slightly yellowish fluid, the whey.