92 WATER 



We know that if we step into water it soaks into and 

 through our shoes. All bodies which allow water to pass 

 into them or through them are called porous, on account 

 of many little holes in them which are called pores. 

 When porous bodies take in water we say that they 

 absorb water. There are other bodies which are porous 

 although they do not seem to be so unless we experiment 

 with them. A brick is very porous, and so are many 

 rocks. As you know, the ground is porous, or the rain 

 would not sink into it. 



Experiment 45. *Porous Bodies Absorb Water. 

 Apparatus: Balance, weights, cake pan. 

 Materials: Sponge, cloth, brick, porous stone. 



a. Weigh the sponge dry, let it soak in water and 

 weigh again. What is the gain in weight? How much 

 water could a pound of sponge take in? 



b. Repeat with the brick. The brick should remain 

 in the water for a full day. 



c. Repeat with the cloth and porous stone. 



The only reason that some bodies are porous is 

 because they contain little holes, or pores. If we wish 

 to keep the water out of a body we must close the holes, 

 just as we close the gate to keep out the dogs or other 

 animals. Preparing material so that it will not permit 

 water to enter is called waterproofing. See Section 74. 



Experiment 46. To Make Porous Bodies Water- 

 proof. 



* Section 59 should precede this experiment. 



