186 THE ARTS AND INDUSTRIES 



It must be remembered, however, that nothing which 

 can burn can be made really fireproof. If the temper- 

 ature is raised high enough the material will burn or be 

 destroyed, no matter what is upon it. Fireproofing 

 serves to prevent easy burning and on that account is a 

 very valuable process. 



74. Waterproofing. 



Many substances are more or less porous and allow 

 water to penetrate them. As we learned in Experiment 

 46, water may be kept out of material by stopping the 

 pores. In that experiment paraffin was used but there 

 are other somewhat similar materials which may be used 

 in the same manner. Thus if the pores of cloth are filled 

 with rubber we obtain what we call rubber cloth. Oil- 

 cloth and oilskins are other examples of the filling of 

 pores of cloth. The foundations and cellar floors of 

 buildings may be made waterproof by covering them 

 with melted tar, or tar paint; by asphalt, and by the 

 addition of other matter to the concrete before it is 

 mixed. 



Another very interesting method is to have the pores, 

 but treat the cloth in such a way that water will not read- 

 ily enter. The following experiment shows the prin- 

 ciple which underlies this method. 



Experiment 77. Waterproofing. 



Apparatus: Burner, ring stand, wire gauze, tin 

 dish, small glass tube, glass. 



Material: Paraffin. 



a. Insert the glass tube in some water in the glass 

 and note how high the water goes by capillarity. See 

 Section 41. 



