1902.] on the Electronic Theory of Electricity. 165 



indicate that the number of molecules of hydrogen in a cubic centi- 

 metre is probably best represented by the number twenty million 

 million million = 2 X 10^^. Hence it follows, since there are two 

 atoms of hydrogen in a molecule, that in electrostatic units the 

 electric charge on a hydrogen atom or hydrogen ion is 



9654^ X_3j< 10^ = ,^- of a C.G.S. electrostatic unit 

 11200 X 4 X 1019 W 



22 

 = -— — - of a coulomb. 

 1020 



Accordingly, if the above atomic charge is called one electron then 

 the conventional British Association electrostatic unit of electric 

 quantity is equal to 1540 million electrons, and the quantity called a 

 coulomb is nearly five million million million electrons. The electron 

 or the electric charge carried by a hydrogen atom or ion is evidently 

 a very important physical constant. If we electrolyse, that is decom- 

 pose by electricity aqueous solutions of various salts, such as sodium 

 chloride, zinc chloride, copper sulphate, silver nitrate, we find, in ac- 

 cordance with Taraday's Laws of Electrolysis, that the passage of a 

 given quantity of electricity through these solutions decomposes them 

 in proportional amounts such that for every 46 grammes of sodium 

 liberated there are 65 of zinc, 63-5 of copper and 216 of silver. 

 These masses are called chemical equivalents. Accordingly, if we 

 imagine a number of vessels placed in a row containing these solutions 

 and by means of platinum connecting links or plates we pass an 

 electric current through the series, for every atom of copper or zinc 

 carried to their respective kathodes, we shall have two atoms of silver 

 or sodium similarly transported. Since the same quantity of 

 electricity must pass through every vessel in the same time, it is 

 evident that the above fact may be interpreted by assuming that 

 whilst an atom of silver or sodium acting as an ion carries one 

 electron, an atom of zinc or copper carries two electrons. 



In the same way we may have atoms which carry three, four, five 

 or six electrons. Thus we may interpret the facts of chemical 

 valency and Faraday's Law of Electrolysis in terms of the electron. 



We are thus confronted by the idea long ago suggested by Weber 

 and by Von Helmholtz, that the agency we call electricity is atomic in 

 structure, that is to say, we can only have it in amounts which are all 

 exact multiples of a certain small unit. Electricity therefore re- 

 sembles those articles of commerce like cigars, which we can buy in 

 exact numbers, 1, 10, 50, 100, 1000, but we cannot buy half a cigar or 

 five-sixths of a cigar. If then the law which holds'good for electricity 

 in association with atoms during electrolysis holds good generally, a 

 very important advance has been made in establishing the fact that 

 there is a small indivisible unit of it which can be multiplied but not 

 divided, and every quantity of electricity, small or large, is an exact 

 integer multiple of this unit, the electron. 



