174 Dr. J. A. Fleming [May 30, 



hydrogen ions and the result is two neutral molecules of water. This 

 combination takes place because the union of oxygen ions with hydro- 

 gen ions to form water evolves more heat and exhausts more potential 

 energy than the combination of oxygen with oxygen and hydrogen 

 with hydrogen ions in equivalent quantity. The energy set free by 

 the union of the O and H is sufficient to continue the dissociation of 

 further gaseous molecules, so the action is explosive and is propagated 

 throughout the mass. 



There is however a broad distinction between the elements in this 

 respect, viz. : that some atoms are prevalently electropositive and others 

 electronegative. A metallic atom for instance is electropositive, but 

 the atoms of non-metals are mostly electronegative. Moreover metals 

 in the mass are electrically good conductors, whereas non-metals in the 

 mass are non-conductors or bad conductors. This may be explained 

 by the varying degree of force required to detach electrons from neutral 

 atoms and conversely the varying degree of attachment of electrons 

 for neutral atoms. Thus we may consider that the metallic atoms 

 lose very easily one or more electrons, and also that there is a some- 

 what feeble attachment in their case between the neutral atom and the 

 free electron. Hence metals in the mass are conductors because there 

 are plenty of free electrons present in them. On the other hand, in 

 the case of non-metallic atoms the force required to detach one or more 

 electrons from the atom is much greater, and conversely the attachment 

 of free electrons for the neutral atom is larger. Accordingly, in 

 non-metals there are few free electrons, and they are therefore non- 

 conductors. Moreover, the presence of positive and negative atomic 

 ions causes them to link together into more or less complex molecules, 

 and they exhibit poly valency and act as the grouping elements in 

 molecular complexes. This is a very characteristic quality of the 

 elements sulphur, silicon and carbon. 



Helmholtz long ago laid stress on the fact that certain physical 

 and chemical effects could only be explained by assuming a varying 

 attraction of electricity for matter. The same idea followed out leads 

 to an hypothesis of chemical combination and dissociation of salts in 

 solution. Thus a molecule of sodic chloride is the electrical union of 

 a monovalent sodium ion or sodium atom minus one electron with a 

 chlorine ion which is a chlorine atom plus one electron. It may be 

 asked why in this case does not the extra electron pass over from the 

 chlorine to the sodium ion and leave two neutral atoms. The answer 

 is because the union between the electron and the chlorine is probably 

 far more intimate than that between the atomic groups. These latter 

 may revolve round their common centre of mass like a double star, but 

 the electron which gives rise to the binding attraction may be more 

 intimately attached to the atomic group into which it has penetrated. 



