(a) By the Specific Gravity Bottle. - Any bottle with a small neck having a fixed mark around the neck can be used in this method. Weigh the bottle when empty (a). Fill with water to the fixed mark and weigh (b). The difference gives the weight of water (b - a). Fill with the required liquid and weigh (c). The difference (c- a) gives the weight of the same volume of the liquid. Then the specific gravity will be

EXAMPLE. - Weight of the empty bottle (a) = 54 g.

 Weight of the bottle filled with water (6) = 304 g.

 Weight of the bottle filled with the liquid (c) = 252.25 g.

Specific gravity bottles are usually made to hold a certain number of grams of water at a stated temperature, and are so marked.

If the bottle holds 1000 g. of water, the specific gravity can be obtained directly. For example, if a thousand-gram bottle holds 1240 g. of hydrochloric acid, then the specific gravity of the acid is 1.240.

 (b) By the Method of Balancing Columns. - A good form of apparatus for this method is that of Hare, shown in Fig. 135. A and B are glass tubes joined at the upper ends to the branches of a Y tube. The other end of the Y is joined to a rubber tube R. The lower end of each tube dips into a liquid in a beaker. C is a clamp and M a meter stick. When pressure is reduced in R the liquids rise to heights that are inversely proportional to their specific gravities. If water is in A and alcohol in B, the specific gravity of the alcohol will be as follows:

the heights to be Height of В' measured from the surface of the liquid in each case.

(c) By the Hydrometer. -A constant-weight hydrometer usually consists of a small glass tube to which two larger bulbs  are sealed. Either mercury or small shot are put into the lower bulb in order to keep the stem of the instrument vertical. For liquids heavier than water the unit mark is placed at the upper end of the stem, which is graduated decimally.

his instrument (Fig. 2) is used by floating it in the liquid in a hydrometer jar, and reading the height to which the liquid stands on the stem.

Special forms of hydrometers are used for special liquids. The alcoholmeter is used for determining the percentage of absolute alcohol in spirits, and the lactometer for testing the purity of milk.

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The Pendulum Method traces the curve. Demonstration

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The Vibration of Plates

The Vibration of Rods and Tubes

Vibration of Air Columns

Nodes and Loops in a Bell

Overtones and Harmonics

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The Sonometer