STRUCTURE OF MATTER 15 



the space containing the gas is made larger, the gas at once fills 

 it, and if it is made smaller, the molecules are simply forced 

 closer together. In some cases, if the gas is compressed 

 enough, the substance may be made to assume the liquid form 

 again. The fact that the free surface of a liquid is absolutely 

 level is often taken advantage of in grading and building. A 

 hose filled with water may be used. The water in one end of 

 the hose will always be exactly level with that in the other 

 (98). 



21. Some Properties of Matter. There are a number of 

 properties which we recognize at once as characteristic of 

 matter. Among these are weight, hardness and brittleness. 

 Other characteristics with which we may not be so familiar 

 are elasticity, tenacity, malleability and ductility. Elasticity is 

 the tendency of matter to return to its original shape and 

 volume after being bent, compressed, stretched, or twisted. 

 Rubber is a very elastic kind of matter, and air is another. 

 Air, it is true, cannot be bent or twisted, but when enclosed 

 in an air-chamber or automobile tire, it has almost perfect 

 elasticity. Tenacity is the capability of a thing to resist being 

 pulled apart. A steel wire has great tenacity. Malleability 

 is the quality of withstanding being hammered out into sheets 

 without cracking and ductility is the capacity of being drawn 

 into wire. Copper is both malleable and ductile; limestone 

 is neither. The metal platinum is so ductile that it may be 

 drawn into a wire scarcely visible to the eye. Gold may be 

 beaten out into sheets so thin that it would require 300,000 

 of them to make a pile an inch high. Not all of the character- 

 istics mentioned are likely to belong to any one substance, 

 or kind of matter, but all substances possess several of them. 

 There are many other qualities that characterize different 

 substances. Some, for instance, may be crystalline, or com- 

 posed of crystals; others may be without definite form, or 

 amorphous. Glass, pitch, paraffin and similar substances are 



