ELECTRONS 91 



comprised of many atoms, which as individuals may 

 have had urges of different degrees of intensity. 



The chlorine atom which serves for visualizing chem- 

 ical activity will also illustrate one fact which remains 

 to be expressed before the picture is complete. Chlor- 

 ine is a substance well known to the chemist. In our 

 modern terms it is the element of atomic number 17, 

 that is, it contains in its nucleus seventeen more protons 

 than electrons. Its atomic number states a difference; 

 but what about the actual content of the nucleus? 



In the first place we know the masses of the proton 

 and electron. The proton is about eighteen hundred 

 and fifty times greater in mass than the electron. It is, 

 therefore, responsibile for the weight of discrete atoms 

 and of their aggregations in such masses as we weigh on 

 chemists' balances or coal-scales. The weight of a 

 helium atom which contains four protons in its nucleus 

 should then be practically four times that of the hydro- 

 gen atom which has a single proton for its nucleus. 

 Oxygen, which is known to contain sixteen protons, is 

 approximately sixteen times as heavy as the hydrogen 

 atom. 



The masses of various atoms have been found by an 

 electrical method by Professor J. J. Thomson and more 

 recently by Dr. F. W. Aston. The method involved 

 ionizing the atoms, that is removing from them one or 

 more electrons. Due to the resulting electrified condi- 

 tion the atom will respond to electrical attractions and 

 repulsions. The amount of its motion may then be 

 used as a measure of its mass just as you might measure 

 masses by observing what motions you could give to 



