VAPOR. 67 



153. DENSITY DEPENDS ON TEMPERA- 



How does tern- 



perature a/ect TURE. If water is boiled in a flask, the 

 density? latter Decomes filled with steam> But? 



although full, more steam can be crowded into the 

 same space. On corking the flask and continuing the 

 heat, the temperature of the water will be raised. 

 Then, forced as it were, by the additional heat, its par- 

 ticles have the power of crowding into the steam be- 

 fore produced, and making it more dense. But after 

 a time, no more can be forced in until the temperature 

 is still further increased. In other words, there is a 

 maximum density corresponding to every temperature. 

 And what is here said of steam, is true of vapor of 

 water produced at lower temperature, and also of other 

 vapors. The higher the temperature, the greater is 

 the density of all vapors, provided a surplus of material 

 is present. But if this is not the case, heat has 

 simply the effect of expanding the vapor as it would 

 an equal quantity of air. In the case of a partial 

 supply of water, the vapor grows more dense, but 

 does not reach the highest density which it would 

 have at the same temperature with a full supply. 

 TI , , 154. DISAPPEARANCE OF HEAT IN VA- 



What remark- 

 able drcum- TORS. The same disappearance of heat 



stance attends , . . 1-1- j 



the formation which occurs when a solid is converted 

 oj- vapors? ^ Q a jjquj^ occurs also when a liquid is 

 converted into a vapor or gas. Thus, if we wish to 

 cool a room in summer, we sprinkle the floor. As the 

 water evaporates, much of the heat of the room dis- 

 appears. It has entered into combination with water 

 to produce vapor, and has no longer the power of af- 



