CHAPTER II. 



COMPOUNDS AND ELEMENTS: MOLECULES AND ATOMS. 



The number of the forms of matter, that is, of the different 

 weighable, space-filling things, in our world reaches an as- 

 tonishing total. 



Two hundred and fifty thousand would, probably, be a 

 modest estimate of the number of things having properties 

 that sharply demarcate them from every other individual 

 thing. It is a simple fact that if one were to attempt to 

 read all the -accounts of the different forms of matter daily 

 discovered, as they appear in the journals of science, one 

 would certainly hopelessly fail, reading twenty-four hours 

 in the day. These substances are known as the " com- 

 pounds" of matter. 



Compounds, however, while they are individual in their 

 properties are not simple in their composition. Common 

 salt may be broken down into a metal that floats on water, 

 called sodium and a greenish-yellow gas called chlorine; 

 prussic acid may be decomposed into two gases called hy- 

 drogen and nitrogen and into a solid called carbon. In fact, 

 every one of this vast number of heterogeneous substances 

 may be broken down successively into simpler bodies that 

 weigh less than the substances from which they are ab- 

 stracted; and these simpler bodies, some seventy in all, 

 constitute the chemist's so-called " elements" of matter. 

 These elements, in their properties, have no relation to the 

 substances which, when united together in various ways, 

 they comprise. Some of them, such as iron, sulphur or 

 phosphorus, may exist free or combined, as the case may 

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