CONSTITUTION OF MATTEE BECQUEREL. 277 



About, the end of the last century an English chemist, Prout, pro- 

 pounded the hypothesis that all elements could be made up by the 

 progressive condensation of hydrogen, the lightest of all the bodies. 



Several years ago, however, modern physicists took a still further 

 step ; they now attribute an atomic structure not only to matter, but to 

 electricity as well, and consider matter as composed of electricity. 



We shall see as a fact that electrified corpuscles have been isolated 

 which themselves appear to be composed of electricit}', entirely free 

 from anything that can properly be termed matter, whose mass is of 

 electro-magnetic origin and is nearly two thousand times as small as 

 that of an atom of hydrogen. 



These atoms of electricity are called electrons. They are present 

 in all bodies ; they are the atoms which are at the source of all phe- 

 nomena of light, and again they are those atoms which allow the 

 conduction of heat and of electricity. The electron appears to> be 

 in the nature of a universal constituent of matter, without being 

 itself matter, in the ordinary sense of the word. 



The first conception of an atom of electricity is a result of the 

 phenomenon of electrolysis, of which you may see an example in 

 the decomposition of acidified water by an electric battery. A solu- 

 tion which is a conductor of electricity and is decomposable by a 

 current is termed an electrolyte. Every molecule of an electrolyte 

 is separable into two atoms or atomic groups, called ions, which 

 possess charges of equal quantity and opposite signs; thus, when 

 sodium chloride is dissolved in water a certain number of molecules 

 dissociate into negative chlorine ions and positive sodium ions. 

 Under the influence of the molecular movements which go to make 

 up heat and consequently from the shocks resulting therefrom there 

 is a constant recombination of the ions and fresh decomposition of 

 the molecules. In a very dilute aqueous solution, however, nearly 

 all the sodium chloride is found to be in a state of dissociation. Now, 

 if two electrodes connected to the poles of a battery are dipped into 

 the solution, the negative ions (chlorine) are carried to the positive 

 pole (anode) and the positive ions (sodium) to> the negative pole 

 (cathode). 



The laws of electrolysis, established by Faraday and worked out 

 completely by Edmond Becquerel have led to the conclusion that all 

 the univalent ions, such as hydrogen, chlorine, sodium, and potas- 

 sium, always carry the same charge (negative or positive), while 

 the bivalent ions (copper and the like) carry a charge just double 

 the preceding, and so on. The charge of the univalent ion is the 

 smallest charge that has ever been observed, and when separated 

 from its material support constitutes the electron or atom of elec- 

 tricity. 



