RECAPITULATION. 



AN ATOM of any element is a particle so small 

 that it undergoes no futher subdivision in chemical 

 transformations. 



A MOLECULE is the smallest particle of matter 

 that can exist in a'free state. 



A SOLID is a substance, the molecules of which 

 are more or less immobile, though probably not in 

 absolute contact. 



A LIQUID is a substance the molecules of which 

 so freely move about each other that it readily as- 

 sumes and retains the form of any vessel in which it 

 is placed. 



A GAS is a substance the molecules of which are 

 so far apart that they seem to have lost all attraction 

 for each other, and, indeed, to have acquired the 

 property of repulsion to such an extent that they 

 are only prevented from receding to a still greater 

 extent by the pressure of surrounding matter. 

 Motion is especially characteristic of gaseous fluids. 



ATOMIC WEIGHTS are, first, the proportions in 

 which elements are found to combine with each 

 other by weight. (The figures showing these pro- 

 portions are purely relative, but all chemists agree 

 to make this relation fixed by giving the number I 

 to hydrogen.) Secondly, they are the weights of 

 equal volumes of elements in the state of gas (rel- 

 ative to i of hydrogen). 



MOLECULAR WEIGHTS These are the weights of 

 equal volumes of gases or vapors, under equal cir- 

 cumstances of temperature and pressure, and rela- 

 tive not to I, but to 2 of hydrogen. In the case of 

 non-volatile bodies, molecular weight is deduced 



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