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<div class="chaptext" id="l15"><SPAN name="less15"></SPAN> <div class="lesson">LESSON XV.</div> <div class="chaphead">HOW VAPOR IS CHANGED TO WATER,</div> <p>Heat, as you have learned, changes water into vapor. You must also know that cold turns vapor back into water again.</p> <table summary="illustration" width="100" border="0" align="left" cellpadding="5" cellspacing="0"> <tr> <td><SPAN href="images/025_l.gif" target="_blank" id="ill25"><ANTIMG src= "images/025.jpg" border="0" alt="THINK OF THE KETTLE WITH THE BOILING WATER." /></SPAN></td> </tr> <tr> <td> <div class="caption">THINK OF THE KETTLE WITH THE BOILING WATER.</div> </td> </tr> </table> <p>Now let us think of the kettle with the boiling water. You will notice a little space; quite close to the spout, where nothing can be seen. Is there no vapor there?</p> <p>Yes, there is vapor there, but it cannot be seen; it is invisible. A little way from the spout we see something white, like smoke. This is only the vapor that has been chilled by the cool air and changed back again into water. The water is in the form of very fine particles, and may be called water-dust.</p> <p>Hold a cold plate over boiling water. Observe how the water-dust gathers into drops that roll down the plate.</p> <p>You have seen the inside of windows in cold weather covered with moisture. Where does it come from? Why did it form there? Why does it sometimes run down on the cold pane?</p> <p>The vapor in our breath turns into water on frosty mornings. Explain this.</p> <p>Carry a pitcher of ice-water into a room, and notice what takes place. A thin mist at once gathers on the outside of the pitcher. What takes place among the little drops of mist? What becomes of these larger drops?</p> <p>Where does the water which collects on the outside of the pitcher come from? Does it come through the pitcher from the inside? Would the same thing have taken place if some other cold object had been used instead of a cold pitcher?</p> <p><i>Write</i> out what you have learned about vapor.</p> </div> <div style="break-after:column;"></div><br />