THE CONQUEST OF NATURE 



of chlorine, although we are justified in thinking of this 

 substance as a whole as composed of sodium-chlorine 

 molecules. It is only by thus visualizing the activity of 

 the atoms in a solution that we are able to provide even 

 a thinkable hypothesis as to the development of elec- 

 tricity in the voltaic cell. 



What puts us on the track of the explanation we are 

 seeking is the fact that the diverse atoms are known 

 to have different electrical properties. In our voltaic 

 cell, for example, sodium atoms would collect at one 

 pole and chlorine atoms at the other. Humphry Davy 

 discovered this fact in the early days of electro-chemistry, 

 just about a century ago. He spoke of the sodium 

 atom as electro-positive, and of the chlorine atom as elec- 

 tro-negative, and he attempted to explain all chemical 

 affinity as merely due to the mutual attraction between 

 positively and negatively electrified atoms. The modern 

 theorist goes one step farther, and explains the negative 

 properties of the chlorine atom by assuming the pres- 

 ence of one negative electron or electricity in excess of 

 the neutralizing charge. The assumption is, that the 

 sodium atom has lost this negative electron and thus has 

 become positively electrified. The chlorine atom, har- 

 boring the fugitive electron, becomes negatively elec- 

 trified. Hence the two atoms are attracted toward op- 

 posite poles of the cell. 



This disunion of atoms, be it understood, must be 

 supposed to take place in the case of any solution of 

 common salt, whether it rests in an ordinary cup or 

 forms a part of the ocean. Here we have, then, material 

 for the generation of the electrical current, if some 



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