The Supply and Uses of Water 233 



SUGGESTIVE QUESTIONS 



1. If the pressure at a certain depth in salt water is 100 pounds per 

 square inch what is the pressure at twice the depth? At three times 

 the depth? 2. A householder finds that water flows with greater 

 force from the faucet at midnight than at midday. Explain. 3. Show 

 that there is less surface in large than in small pipes in proportion to 

 the amount of water carried by the pipe. 4. If water were used at 

 the same rate at all times during day and night would a standpipe 

 be of any use? 5. What different devices do you know by which 

 water pressure is increased in emergencies, as for a fire? 6. If there 

 were no leaks and no water being used in a city system of water pipes 

 and the pressure were increased at the pump from 20 to 40 pounds per 

 square inch how much change of pressure would there be in distant 

 parts of the system? 



7. Boilers are tested by filling them with water, then forcing into 

 them a little more water. If by one stroke of the pump, after the 

 boiler is filled, the pressure at the pump is increased by fifty pounds 

 per square inch, what increase in pressure is thereby given to each 

 square inch of the inner surface of the boiler? If the boiler were 

 filled with air, would each stroke of an air pump of the same size in- 

 crease the pressure on the inner surface at the same rate? Explain 

 the difference. If the pressure were increased to the bursting point, 

 which of the two substances, water or air, would cause a dangerous 

 explosion ? 



X. WATER POWER 



97. Importance of power. The things required by man to 

 satisfy his needs are produced by very complex activities, 

 directed by men who are familiar with, and in some degree 

 masters of, the resources of nature. The whole earth, through 

 farm, forest, mine, river, lake, sea, and air, is made to give of 

 its raw materials and to supply the power whereby manufactur- 

 ing, transportation, and communication are made possible. Of 

 the whole complex system of modern life and industry the power 

 plant, without which machinery and appliances would be useless, 

 is the central organ. 



98. Sources of power. The power plant to-day derives its 

 energy from three main sources, fuel, water, and wind. Of all 

 fuels, coal furnishes about 75 per cent, and oil, natural gas_, 



