i 9 8 SCIENCE PROGRESS 



This is a minor matter, it is true, but it leads Prof. Arm- 

 strong to liken a radium atom to a molecule of nitrogen 

 chloride, a compound which explosively resolves itself into 

 what are called its " constituent " atoms ; although in what form 

 the nitrogen and the chlorine exist in the compound, is a matter 

 on which I would gladly learn from Prof. Armstrong rather than 

 attempt to instruct him. 



But it is misleading to liken the progressive disintegration- 

 process responsible for radioactivity to the ordinary decom- 

 position of chemical compounds. Prof. Armstrong admits that 

 the rupture of a radium atom involves the formation of two 

 neutral substances, the Emanation and Helium ; but he goes on 

 to say that " it cannot be a compound of such substances, and 

 yet they are obtained from it " ; so he supposes that " either or 

 both must be present in it in some active form." 



This guess is made merely because he is unwilling to 

 recognise any mode of grouping other than a chemical one — i.e. 

 other than a grouping of atoms under chemical affinity. Radium 

 is truly not a chemical compound, but its atoms appear to 

 embody a physical grouping such that definite substances 

 result when it subdivides. This might be speculation, were it 

 not that the emission of observed substances from radium 

 actually occurs. In no chemical decomposition are atoms 

 shot out with one-tenth of the velocity of light. The energy' 

 displayed is of a different order from chemical energy. 



In the effort which he makes to liken this kind of volcanic 

 disruption to chemical decomposition, on the analogy of 

 nitrogen chloride, Prof. Armstrong is forced into hypotheses 

 for which there is no basis whatever beyond his own speculative 

 instinct. This is what he says : 



" 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 protohelium, 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. . . . Protohelium apparently is the wondrous material 

 at the root of radioactivity." 



