654 SCIENCE PROGRESS 



two absolutely neutral substances apparently. It cannot be a 

 compound of such substances and yet they are obtained from 

 it : either or both must be present in it in some active form. 

 Many parallel cases are known to us. When nitrogen chloride 

 is exploded, it gives rise to nitrogen and chlorine gases, neither 

 of which can conceivably be present as such in the chloride : in 

 point of fact, there is every reason to believe that the molecule 

 of the chloride is resolved into its constituent " atoms" and that 

 these then unite in new ways to form molecules : it is in this 

 last operation that the energy is liberated. Thus 



2 [NC1 3 = N + CI + CI + CI] 

 N + N = N 2 

 3[Cl+ C1 = C1 2 ] 



It is only necessary to suppose that the molecule of Helium 

 as we know it, like the molecule of nitrogen as we know it, is 

 composed of several " atoms " of — let us call it — protohclium and 

 that the atoms of protohelium have intense affinity for one 

 another — an affinity so intense that it is far beyond anything we 

 have experienced in the case of any other element. 



When argon was first described in 1895 by Rayleigh and 

 Ramsay, I ventured to assert such a view in explanation of its 

 apparently complete inactivity. What is true of argon, is 

 true doubtless of all its companions in air — helium, neon and 

 krypton. 



In the light of my hypothesis, chemical primaries such as 

 Uranium, Thorium and Radium are comparable with the com- 

 plex hydrocarbons of the paraffin series represented generally 

 by the formula C n H 2n + 2 . When the paraffins are heated, they 

 are decomposed in a variety of ways : one way is that, time after 

 time, the elements of a molecule of hydrogen are removed, a 

 hydrocarbon being produced containing proportionately less 

 hydrogen ; thus 



C11H211 + 2 = CnHin + H2 



CuH'in = CnHo n _ 2 + H2J etc. 



Such changes correspond to those which the radioactive 

 primaries undergo in losing the elements of a molecule of 

 helium time after time. But some of the immediate products in 

 the case of the hydrocarbons are unstable and at once undergo 

 change into an isomeric substance ; this is a weightless change 







