WATERPROOFING 93 



Apparatus: Burner, ring stand, wire gauze, tin 

 dish. 



Materials: Piece of cloth, 4"x5", paraffin. 



a. Melt the paraffin by gentle heat and dip the 

 cloth into it. While the paraffin on the cloth is still 

 warm, shape the cloth into a four-sided box. When cold 

 it should hold water. What keeps the water from going 

 through the cloth? 



Rubber is the material which is commonly used to 

 fill the pores of porous material, in order to make it 

 waterproof, as rubber is not altered by ordinary changes 

 in temperature. Do you think that your box would 

 hold hot water? 



While it is not pleasant to have water come through 

 our clothing or even our houses, the porosity of materials 

 has its use. Water which passes through the small pores 

 has lost a large amount of its dirt. The separation of 

 dirt from water, by means of porous bodies, is called 

 filtration, and the porous body is called a filter. All 

 water which comes from the earth in springs and wells 

 has been filtered by passing through the porous ground. 

 We can filter water, where necessary, by means of porous 

 dishes or porous paper. 



Experiment 47. Filtration. 



Apparatus: Funnel, funnel-holder (cut a hole in the 

 small end of a chalk box), test tubes. 



