260 



GENERAL SCIENCE 



such as a small cannon ball; or a croquet ball loaded with metal will answer 

 the purpose. If a small ball is used, place the ball hi a graduate so as to meas- 

 ure the amount of water displaced or pushed aside. The increase in height of 

 the water in the graduate will show the amount of water displaced by the ball. 

 Weigh an equal amount of water. Weigh the ball in water. Compare the 

 weight of the water with the loss of weight of the ball. If the croquet ball is 

 used, fill a dish as full of water as it will hold. Place the ball in the dish, catch- 

 ing in a pan the water which overflows. Weigh the water which has been dis- 

 placed by the ball. Compare the loss of weight of the ball with the weight 

 of the water displaced. 



A body floats when it sinks into a liquid to such a point that 

 the weight of the liquid displaced by the body is equal to the weight 

 of the body. If the body can not displace enough water to equal 

 its own weight it sinks, but it loses as much weight as the weight of 

 the water it displaces. 



A ship weighing 50,000 tons must push aside 50,000 tons of water. 

 A cubic foot of water weighs about 62 \ pounds. If a body displaces 

 a cubic foot of water, it loses 62 J pounds of its weight. Because of 

 these facts, architects and engineers are able to tell the weight of 

 granite piers, steel columns, etc., without weighing them, since 

 they know how many times heavier than water each cubic foot 

 of material is. 



Submarines as Sinking and Floating Bodies. An excellent illus- 

 tration of how the submarine sinks and floats is the bobbing bottle. 



Fill a flat-sided quart bottle full of water, and invert 

 in it a small pill bottle containing enough water to just 

 allow it to float. Cork the bottle^ and adjust the stop- 

 per so that the little bottle inside will just float. Press 

 on the sides of the big bottle. Since the glass is elastic, 

 the sides will give slightly, forcing water up into the 

 little bottle, and slightly compressing the air. The 

 bottle will sink. If the pressure is relieved, the com- 

 pressed air will expand, forcing the water out of the 

 little bottle which will rise. 



A submarine has large air tanks into which 

 FIG. 164. water is pumped to make the submarine sink. 



When the submarine wishes to rise the water is 

 forced out. The submarine then displaces a weight of water greater than 

 its own weight a result which causes it to rise to the top and float. 



