HOW MATTER CHANGES 141 



makes a large volume of gas. The rapid expansion of this 

 gas produces the desired explosion. Gunpowder, the ex- 

 plosive longest in use, contains saltpeter to furnish oxygen, 

 and charcoal and sulphur for combustibles. 



152. The Relation of Oxidation to Life. The unfold- 

 ing of a flower bud, the turning of a leaf toward the sun, the 

 lifting of the foot or the hand, the beating of the heart, are all 

 forms of work and therefore require energy. Energy in 

 living things is the result of oxidation, and all living things 

 use oxygen to produce energy. Part of the energy shows 

 itself as heat or increase in body temperature a temper- 

 ature which is higher in many animals than in plants. 



Life ceases when no energy is produced. That is why 

 suffocation, or lack of air, produces death. Drowning is a 

 form of suffocation. The loss of life in a burning building is 

 not always the result of burning to death; it is often due to 

 suffocation. Irritating, suffocating gases are made by the 

 burning of wood, as we all know if we have ever sat near a 

 smoking fireplace. Such gases in a burning building may 

 fill rooms and stairways not touched by fire. One of the 

 first effects of suffocation is unconsciousness. If the victim 

 is rescued and supplied with fresh air, fatal results may be 

 prevented. 



When injurious gases, as coal gas or illuminating gas, are 

 mixed with air, the result is not simply suffocation but a 

 poisoning. This is called asphyxiation. 



153. The Ignition Point. The temperature which a sub- 

 stance must have before it takes fire, or ignites, is called the 

 kindling point or ignition point. The kindling point of gaso- 

 lene vapor is so low that it is not safe to use gasolene in a 

 room where there is a fire or flame of any kind. Alcohol 

 also has a very low ignition point. Hot alcohol is some- 

 times recommended for treatment of bruises, but the alcohol 

 cannot safely be placed in a dish on the stove; it may, 

 however, be heated over a dish of hot water. 



