CHAPTER VIII 



CHEMICAL PHENOMENA 



Physical and chemical properties. Many so-called 

 properties of a substance can be noted without causing 

 the substance to undergo chemical change, and are there- 

 fore called its pliysical properties. Among these are its 

 physical state, color, odor, taste, size, shape, and weight. 



Other properties are discovered only when a substance 

 undergoes chemical change. These are called its chemical 

 properties. We know, for example, that wood burns in 

 air ; that carbon dioxide turns lime water milky ; and that 

 iron rusts when exposed to the air. 



Classification of matter. At first sight there appears 

 to be no limit to the varieties of matter of which the 

 world is made. For convenience in study we may 

 classify all these varieties under three heads; namely: 

 mechanical mixtures, chemical comppunds, and 

 elements. 



Mechanical mixtures. If equal amounts of salt and 

 iron filings are thoroughly mixed together, the result- 

 ing product has the appearance of a new substance. 

 If it is examined more closely, however, it will be seen 

 to be merely a mixture of salt and iron, each of which 



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