CHAPTER IV. 



PROPERTIES OF SOLIDS, LIQUIDS AND GASES. 



THE resistance which a substance offers to the separation of its 

 parts by pulling is called tenacity. This property varies greatly 

 in different substances, cast steel being the most tenacious sub- 

 stance known. Tenacity differs from toughness; the cast steel 

 will bear a pulling strain but will not bear much twisting or 

 bending backward and forward, while copper, which is not as 

 tenacious as the steel, will bear twisting and bending many 

 times before breaking, having the property of toughness in a 

 higher degree. Cast steel does not stretch. Other substances, as 

 copper, soft steel and iron, gold, silver, etc., yield to the pull- 

 ing force and may be drawn into wire, thus exhibiting the prop- 

 erty of ductility. This property varies greatly in different sub- 

 stances, and many substances which are but slightly ductile when 

 cold possess that property in a high degree when heated, as glass 

 and iron. The tenacity of a substance is increased by drawing it 

 out into wire. Thus the cables of suspension bridges are made 

 of fine wire twisted together, not only because such form makes 

 them flexible, but because the steel, in that form, possesses more 

 tenacity. Platinum is the most ductile of metals. Gold and 

 silver also possess this property in a high degree, while lead and 

 tin are only slightly ductile. 



Malleability is a property similar to ductility, which allows a 

 body to be rolled or hammered into plates or thin sheets. Gold 

 is the most malleable substance known. Most of the metals 

 possess this group of properties in some degree. 



Hardness is that property of solids which enables them to 

 resist any action which tends to abrade or scratch them. Hard- 

 ness does not mean strength, indeed hard substances usually 

 possess the property of brittleness as well, yielding easily to a 

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