LIQUIDS AND THEIR PROPERTIES 



89 



pressure upon the top is equal to the weight of (2X2X3) 

 12 cubic centimeters of water. The total upward pressure 

 on the bottom of the block is equal to the weight of 

 (2 X 2 X 5) 20 cubic centi- 

 meters of water. The total 

 pressure upon each side 

 of the block is equal to the 

 weight of (2X2X4) 16 

 cubic centimeters of water . 

 The third law of pres- 

 sure is applied in the 

 construction of hydraulic 

 presses and elevators. 

 Water enters, or is 

 pumped into, the small 

 cylinder with a force, for 

 example, of 100 grams to 

 the square centimeter of 

 area. The water at the 

 bottom of this cylinder 

 has that pressure upon it. 

 Because the pressure is 

 exerted in every direction, 

 the water at the same 

 level in the large cylinder 

 receives a pressure of 100 

 grams to the square centi- 

 meter. This pressure, in 

 turn, is exerted upward 

 as well as horizontally 

 upon the water and upon 

 each square centimeter of 3 - Fr m wh i ch 



stove? 4. Trace 



the piston in the large 

 cylinder. If the area of 

 the large piston is 900 



FIG. 39. GRAVITY PRESSURE IN A 

 HOT-WATER BOILER 



1. Under what conditions is an 

 elevated water tank necessary to a hot- 

 water system? 2. If a tank is not needed, 

 where does the water enter the boiler? 



does {i e t nteT ^ e 



its course from the 

 water-front of the stove to a story above 

 the boiler. 5. Name in order the changes 

 of direction of pressure from the street 

 to the stove. (Use upward, horizontal.) 



