SOME UNFAMILIAR FORMS OF BURNING 49 



accompanied by the fire and smoke so familiar to us, but the 

 process is none the less burning, or combination with oxygen. 

 Burning which is not accompanied by any of the appearances 

 of ordinary burning is known as oxidation. 



The tendency of iron to rust lessens its efficiency and 

 value, and many devices have been introduced to prevent 

 rusting. A coating of paint or varnish is sometimes applied 

 to iron in order to prevent contact with air. The galvanizing 

 of iron is another attempt to secure the same result ; in this 

 process iron is dipped into molten zinc, thereby acquiring a 

 coating of zinc, and forming what is known as galvanized 

 iron. Zinc does not combine with oxygen under ordinary cir- 

 cumstances, and hence galvanized iron is immune from rust. 



Decay is a process of oxidation ; the tree which rots slowly 

 away is undergoing oxidation, and the result of the slow 

 burning is the decomposed matter which we see and the 

 invisible gases which pass into the atmosphere. The log 

 which blazes on our hearth gives out sufficient heat to warm 

 us ; the log which decays in the forest gives out an equivalent 

 amount of heat, but the heat is evolved so slowly that we are 

 not conscious of it. Burning accompanied by a blaze and 

 intense heat is a rapid process ; burning unaccompanied by 

 fire and appreciable heat is a slow, gradual process, requiring 

 days, weeks, and even long years for its completion. 



Another form of oxidation occurs daily in the human body. 

 In Section 35 we saw that the human body is an engine 

 whose fuel is food ; the burning of that food in the body 

 furnishes the heat necessary for bodily warmth and the 

 energy required for thought and action. Oxygen is essential 

 to burning, and the food fires within the body are kept alive 

 by the oxygen taken into the body at every breath by the 

 lungs. We see now one reason for an abundance of fresh 

 air in daily life. 



CL. GEN. SCI. 4 



