ii2 Common Science 



When you are cooking potatoes, are you trying to 

 keep them very hot or are you trying to boil the water 

 away from them ? Which are you trying to do in making 

 candy, to keep the sugar very hot or to boil the water 

 away from it? 



All the extra heat you put into boiling water goes 

 toward changing the water into steam ; it cannot raise 

 the water's temperature, because at the moment when 

 water gets above the boiling point it ceases to be water 

 and becomes steam. This steam takes up much more 

 room than the water did, so it passes off into the air. 

 You can tell when a teakettle boils by watching the spout 

 to see when the steam 1 pours forth from it in a strong, 

 steady stream. If the steam took no more room than 

 the water, it could stay in the kettle as easily as the 

 water. 



Distilling. When liquids are mixed together and dis- 

 solved in each other, it looks as if it would be impos- 

 sible to take them apart. But it isn't. They can usually 

 be separated almost perfectly by simply boiling them 

 and collecting their vapor. For different substances boil 

 at different temperatures just as they melt at different 

 temperatures. Liquid air will boil on a cake of ice ; 

 it takes the intense heat of the electric furnace to boil 

 melted iron. Alcohol boils at a lower temperature than 

 water ; gasoline boils at a lower temperature than kero- 

 sene. And people make a great deal of practical use of 



1 What you see is really not the steam, but the vapor formed as the 

 steam condenses in the cool room. The steam itself is invisible, as you 

 can tell by looking at the mouth of the spout of a kettle of boiling water. 

 You will see a clear space before the white vapor begins. The clear 

 space is steam. 



