CHAPTER VIII 

 PROPERTIES OF GASES 



84. Gas Pressure and Industry. There are many tools 

 driven by air pressure, and there are a number of devices 

 that depend upon the properties of gases for their action. 

 Therefore intelligent knowledge of trade work frequently 

 depends upon an understanding of some of the fundamental 

 properties of gases. 



85. Three States of Matter. Ice, water, and steam re- 

 present the three states of liquid matter. A block of ice has 

 a definite form and volume. Water has a free, level surface, 

 but assumes the shape of the containing vessel. Steam has 

 neither shape nor volume. Notice the steam escaping from 

 a kettle or from the exhaust pipe of a power plant, and see 

 how it tends to spread out when released from the containing 

 vessel. Almost all substances can be transformed into a 

 solid, liquid, or gaseous state by suitable changes in tem- 

 perature. We may summarize the characteristic differences 

 of these three conditions by saying that solids have per- 

 manent form and volume; that liquids have no permanent 

 form, but have a definite, volume; while gases have neither 

 permanent form nor permanent volume. 



All gases tend to spread out or diffuse themselves and this 

 tendency causes them to exert considerable pressure equally 

 against the sides of the vessels holding them. If a piston were 



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