WATER A SOURCE OF FIRE. 



developed by transformation of the moving 

 energy with which two masses of matter clash 

 together, so that a small piece of iron between 

 the hammer and anvil can be made red-hot 

 by blows of the former. 



In a somewhat similar manner heat is deve- 

 loped of much greater intensity when the mole- 

 cules or atoms of elements which are said to 

 have a strong affinity for each other rush 

 violently together in the act of re-combination. 



In the present instance the oxygen rushes 

 into combination with the sodium or potassium 

 so energetically and with the development 

 of so much heat as to set fire to the hydrogen 

 which is being set free at the same time. The 

 result is a hydrogen flame maintained, instead 

 of being put out, by the application of water 

 to the metal. 



Alcohol, which is a source of so much heat 

 in other ways, is anything but cooled by throw- 

 ing cold water upon it. The two substances, 

 on being mixed, unite with so much energy 

 that the addition of pure alcohol to an equal 

 quantity of water, neither hotter nor colder 

 than itself, results in a distinct rise of tem- 

 perature. 



The same thing occurs still more power- 

 fully on the union of water with sulphuric 

 acid, or with caustic potash or soda. The 

 resulting heat is indeed so great in these cases that 

 therejs^danger^orajglass vessel being cracked, 



205 



