SECTION II. 



OF THE NATURE AND PROPERTIES OF STEAM, ITS ELASTIC FORCE, 

 EXPANSIVE FORCE, AND POWER OF MOTION. 



ART. 65. NATURAL bodies exist in three states ; the solid, the liquid, and the 

 gaseous. The state of many of them may be changed : thus, water may be in the 

 solid state as ice, in the liquid as water, in the gaseous as steam, and these 

 changes take place only under particular degrees of heat and pressure ; but there 

 are some gaseous bodies which cannot be reduced to the liquid form by the means 

 we at this time are acquainted with ; though there has been so much accomplished 

 as to render it tolerably certain, that all the gases known would be reduced to 

 liquids, were they exposed to sufficient pressure and reduction of temperature. 



66. Those gases which are not changed into liquids by the ordinary changes 

 of temperature and pressure, are called PERMANENT GASES. 



The gases which condense into liquids by the common changes of temperature 

 and pressure, are called VAPOURS, or STEAMS : we shall use the term ' steam' in 

 preference to 'vapour.' 



67. Heat, free and uncombined, is diffused through all bodies in nature, 

 whether they be in the state of solids, liquids,' or gases ; and it constantly tends to 

 an equilibrium ; so that, when by any means it is accumulated in particular sub- 

 stances, a portion is quickly given off to the surrounding bodies, so as to bring the 

 whole to one common temperature. On the other hand, where bodies have been 

 deprived of a portion of it, heat is given off to them by, or heat passes to them 

 from, the surrounding bodies, to restore the equilibrium. 



68. When there is an equilibrium of heat, or the adjoining bodies are of the 

 same temperature, if it be destroyed by the introduction of a fresh quantity of heat, 

 different bodies will be found to absorb different quantities of the new portion of 

 heat in restoring the equilibrium. The peculiar quantity which each body absorbs 

 under the same circumstances, is denominated the SPECIFIC HEAT of that body. In 



