ICE, WATER, AND STEAM 



107 



as much space as the liquid water from which it was formed. 

 Since steam occupies so much more space than water, it is 

 of course correspondingly lighter. It is in fact lighter than 

 air. If water is boiled in a closed vessel (as in a steam boiler), 

 the steam cannot expand, but as the temperature increases, 

 the pressure also increases, and finally the steam finds some 

 way of escape, either by breaking the boiler or through some 

 means provided for its escape, as through a safety valve. This 

 power of expansion is utilized by means of the steam engine. 



FIG. 58. Distillation 



The solution to be distilled is placed in A ; the steam which passes through the 

 tube is condensed in B, which may be cooled with ice or snow 



Steam is a transparent, colorless gas. When steam escapes 

 into the air, there is always a white cloud. This cloud is not 

 steam. The steam quickly cools to a temperature near that 

 of the air, and this is so much below the boiling point that 

 the steam returns to the liquid form. The white cloud is 

 made up of many little drops of liquid water. 



As the steam is emerging from the spout of a teakettle in 

 which water is boiling, it may be observed that the steam is 

 transparent as it passes from the end of the spout. In this 

 transparent area the steam has not yet condensed (fig. 56). 



