EXPERIMENT 7: PRESENCE OF GASES IN WATER.—Fill a beaker half full of water, and note its temperature. Heat the water, and observe the changes which take place. What appears on the sides and bottom of the beaker? What does water contain which is driven off by heat?
EXPERIMENT 8: SIMMERING AND BOILING OF WATER.—Continue to heat the water of Experiment 7 until the larger bubbles form and disappear at the surface of the water. Note the temperature. Continue to heat the water until bubbling occurs on the surface of the water. Note the temperature. What is indicated by the larger bubbles?
HEATING WATER.—When bubbling occurs below the surface, water is simmering. When the surface is in motion and steam is given off, water is boiling.
[Illustration: FIGURE 19—SCENE ON A TEA PLANTATION.]
The loss of gases makes boiled water taste flat or insipid. This flatness can be overcome somewhat by aerating the water after boiling, i.e. by pouring it from one vessel into another and thus mixing air with it.
TEA AND ITS SELECTION.—Tea shrubs grow in India, Ceylon, China, and Japan (see Figure 19). The buds and leaves of these shrubs are cut and dried and sold as tea.
In buying tea the size of the dried leaves should be noted. The smallest leaves are those which have grown nearest the tip of the twig and hence are the youngest. These make the choicest tea. The older and larger leaves make tea of less fine flavor. "Flowery Pekoe" and "Orange Pekoe" are choice India teas. These brands consist of the buds and youngest leaves.
Another point to consider in buying tea is its color. Tea leaves are either black or green. The chief difference between black and green tea is that black tea leaves are fermented after picking, while green are not. Tea leaves contain flavoring and stimulating materials and a substance called tannin (sometimes called tannic acid) which interferes with digestion. The presence of tannin in both black and green tea can be shown by the following:
EXPERIMENT 9: TANNIN IN TEA.—(a) Put 1/2 teaspoonful of black tea in a cup. Add 1/2 cupful of boiling water. Let it stand for 5 minutes, then strain the infusion.
(b) Repeat (a) substituting green tea for black.