in Pascal's Law.

affects the result.

Neither size, nor shape, nor position It is in accordance with this principle that water" seeks its own level," that fountains play, and that water is distributed in city waterworks.

145. Superposed Liquids. If two or more liquids which have different densities and will not mix are poured into a jar, they will come to rest in the order of their densities, with the surfaces of each separating them horizontally. Mercury, water, oil, and alcohol, when poured into a test tube, will come to rest in the order named. If they are to be poured in in such a way that the alcohol and water can come in contact, the water should have dissolved in it some sodium carbonate. It is an easy matter to find a solid that will sink through one liquid layer and float on another, as a bicycle ball on the top of the mercury and at the bottom of the water.

-Mercury

FIG. 123

146. The Hydraulic Ram is used for the purpose of raising water to a greater height than its source.

The machine shown in Fig. 124 uses the water from

a stream or lake to force pure spring water into an elevated tank. A is the drive pipe connected with the water supply, a few feet above the ram. I is the pure water

pipe, and P is the service pipe which carries the water to the tank. The water flows in through pipes A and I, and out through the valve B, until the pressure due to the increasing velocity is enough to close B. When this valve closes, the momentum of the moving water produces what is called the "ramming stroke," which opens the valve C, and forces water into the air chamber D until the pressure of the air in P is equal to the pressure of the water in A. When this occurs, the flow through C is reversed, the valve closes, and the operation is then repeated.

A proper adjustment of the quantities of water in A and I respectively must be made so as to insure that only pure water can flow into D. If the water coming down A is pure enough to be sent into the tank, I is removed, and H is closed Dynamo with a screw plug.

147. The Turbine Water Wheel is another, more important, machine for utilizing the pressure of a column of water. The well-known form of lawn sprinkler which throws water in small streams from holes in one side of each of four revolving arms, is a simple reaction turbine. The rotation is produced by the reaction of the air and the difference in pressure on the opposite sides of the tube. A jet of water directed against the paddles of a paddle wheel so as to bine make it rotate by the force of the impact would illustrate the principle of an impulse turbine. Both principles are used in turbine water wheels, which are made in various forms.

At Niagara Falls water goes from the vertical penstock into the central part of a horizontal wheel and passes outward between fixed guides, G, Fig. 126,

which direct it against the vanes V attached to the rotating part of the wheel. The motion may be produced either by the impact upon V in the direction of the heavy arrow, or by the reaction as the water leaves the wheel in the opposite direction. The wheel rotates a vertical shaft connected with the dynamo at the top of the wheel pit (Fig. 125).

FIG. 126

In another type of turbine, the water enters the outer part of the wheel through fixed guides, and leaves the inner part through moving vanes.

Questions

1. Why do liquids exert pressure on submerged surfaces? What governs the amount of this pressure?

2. State the rule for finding the pressure on any submerged surface.

3. State Pascal's Law.

4. Name the essential parts of a hydraulic press.

5. State the law of the hydraulic press. Can oil be used to operate it as well as water?

6. If the areas of the large and small pistons of a hydraulic press are to each other as 20 is to 2, how would the total pressures exerted on each compare? How would the pressures per square inch on each compare? How would the distances moved through by each compare?

7. Why would not air answer so well as water in a hydraulic press? 8. Why is a dam built with the base thicker than the top? Why is the upper face usually made slanting up stream?

9. What determines the pressure at the nozzle of a fire hose when it is connected directly to the hydrant?

10. If oil and water are shaken together in a test tube and it is then set aside, what will happen? Why?

11. Why is an air chamber used in a hydraulic ram?

12. What is the direction of the pressure of water on the walls of the vessel that contains it?

13. A hole 2 ft. long and 1 ft. wide is broken in the side of a ship. What would be the result of weighting a piece of heavy sail cloth with a piece of iron at each of the two corners and letting it down the side of the ship over the hole?

Problems

1. If the power arm of the lever in Fig. 112 is 26 in., and the resistance arm 6 in., how much pressure will be exerted on the inside of the bottle, which has a surface of 20 sq. in., if the stopper is 1 inch in diameter and the power is 6 lb.?

2. In Fig. 113, what would be the upward pressure on B if the downward pressure on A were 60 lb., the surface of base of A 4 sq. in., and that of base of B 256 sq. in.?

3. The small plunger of the hydraulic press shown in Fig. 113 is 2 in. in diameter and the large plunger is 14 in. in diameter. What upward pressure on B will a power of 30 lb. exert if the lever is 3 ft. long and the distance from the plunger to the fulcrum is 5 in.?

4. A tank is 1 ft. square and 2 ft. deep. If filled with water, what is the pressure on the bottom and on each of the four sides?

5. What would be the total pressure if the tank were filled with mercury, the mercury being 13.6 times as heavy as water?

6. A swimming tank 70 ft. long and 30 ft. wide has a bottom which is 8 ft. deep at one end and slopes to the surface of the water at the other. What is the pressure on the bottom, sides, and end?

FIG. 128

7. The steel water tank shown in Fig. 128 has an internal diameter of 22 ft. The height of the cylindrical portion is 28 ft., and the bottom is a hemisphere. When the tank