36 



A YEAR IN SCIENCE 



begins again. This rise continues until a temperature 

 of 100 C. is reached. Then the mercury in the ther- 

 mometer again becomes stationary. This time the 



Fig. 19. When water is heated it changes to a gas, which as it 

 escapes, forms bubbles in the water. This water vapor is transpar- 

 ent when it is, in the flask, and also where it issues from the end 

 of the tube. As soon as it cools^ it again condenses in the form 

 of steam. 



water is being changed into steam. When the water 

 has all been converted into steam, the mercury again 

 rises, provided the steam is in a vessel from which it 

 can not escape. 



