50 SCIENCE PRIMERS. [MATERIAL 



32. Increase of Heat at length causes 

 Water to become Steam. 



Thus a change is effected in the properties of water 

 by heating it ever so little. If it is more strongly 

 heated a still greater change takes place. You 

 know what happens when a saucepan containing 

 water is put on the fire. The water gets hotter and 

 hotter, then it begins to simmer, and finally, when 

 it reaches 212, it boils away into steam, which passes 

 into the air and disappears. If the boiling is carried 

 on long enough all the water vanishes. It looks at 

 first as if the water had been destroyed by the heat. 

 In reality, however, not a particle of water has been 

 destroyed. It has merely changed its state. The 

 heat has altered it from the state of liquid water into 

 that of gaseous water, vapour or steam. 



Try the same experiment with a tea-kettle instead 

 of a saucepan, but only put a little water in the tea- 

 kettle, and shut the lid well down. Then, as soon as 

 the water begins to boil, the steam will shoot out of 

 the spout in a jet ; and this will go on as long as any 

 water remains in the kettle. 



The steam, as it comes out of the spout, is so hot 

 that it will scald you if you put your finger in it. But 

 you may satisfy yourself that it is very hot, without 

 scalding your fingers, by holding a stick of sealing-wax 

 in it. The wax will soften, just as if you held it before 

 the fire. Moreover, if you look through the steam, just 

 where it leaves the spout, you will see that it is quite 

 transparent; it is only at some little distance from 

 the spout that it loses its transparency, changes into 

 a white opaque cloud, and rapidly vanishes in the air. 



