22 INTRODUCTION. 



with steam. Upon now introducing into the flask a second and 

 third liquid for instance, alcohol and ether, we find that of each 

 of these liquids exactly the same quantity will evaporate which 

 would have evaporated if these liquids had been introduced into 



the empty flask. This fact will undoubtedly prove that there 

 must be small particles of steam which are not in close contact, 

 that there are spaces between these particles which may be 

 occupied by the particles of a second, third, or more substances. 

 And to these particles of matter we give the name molecules, 

 and the spaces between them we call intermolecular spaces. 



We have thus demonstrated the correctness of the so-called 

 molecular theory, but the proof given is but one of many. Of 

 these molecules (though individually by far too small to make 

 any impression whatever upon our senses), our conception is so 

 perfect, that we even have formed an idea of the actual size of 

 these minute particles of matter. Very good reasons lead us to 

 believe that the diameter of a molecule is equal to about 

 f one inch, and that one cubic inch of a gas under 



ordinary conditions contains about one hundred thousand mil- 

 lion million millions of molecules. 



These figures at first glance appear to be beyond the limit of 

 human conception, but in order to give some idea of the size of 

 these molecules it may be mentioned that if a space of water as 

 large as a pea were to be magnified to the size of our earth, 



