OXYGEN OF THE AIR. 25 



by combinations between an alkali on one side and 

 an acid on the other. In short, the all-pervading 

 oxygen is ever ready to take hold of anything that 

 conies along, changing it in form and nature. 



Combustion — the burning and apparent destruc- 

 tion of any substance — as already stated, is nothing 

 more than its chemical combination with oxygen. 

 Close the draft of a stove so tight that no more air 

 is admitted to the burning material, and burning 

 will cease. Oxygen is also indispensable for respir- 

 ation, as this is merely a burning process, or a com- 

 bination of oxygen with carbon, by which animal 

 heat is generated, much in the same (though less 

 violent) way as heat in a furnace. Shut off the 

 supply of oxygen to the lungs, and the animal fire, 

 called ''life," comes to a sudden stop. This oxygen 

 is the most common substance on earth. Eight 

 ninths of the water and a large share of the rocks 

 and minerals consist of oxygen in chemical combina- 

 tion. In the atmosphere we have it combined, 

 merely in mixture with nitrogen, and the latter 

 seems to serve the purpose of a dilutent, simply. 

 Clear alcohol, when used as a beverage, would soon 

 kill the hardest drinker; but many persons who 

 indulge in that article, largely diluted, (although I 

 would not dare to recommend the practice) live to a 

 good old age. So would clear oxygen stimulate 

 the life forces to excessively hasty action, and hurry 

 up the change of tissue much faster than nutrition 

 could restore it, thus crowding a number of years 

 of one's life into one. A great dilution is absolutely 

 necessary, and the diluting medium, nitrogen, forms 

 four fifths of the atmosphere. 



