774 Sir J. J. Thomson on the 



acid are o£ the type in which there is intra-molecu.ar 

 ionization. In cases like these the further chemical com- 

 bination goes on the greater will be the number of the 

 nuclei which promote the combinatian ; there will evidently 

 be a tendency for reactions of this type to become explosive. 

 The condensation of the gas round a molecular doublet 

 such as occurs in water is, on this view, due to the strong- 

 electric force round the doublet. If instead of a molecule 

 with its doublet we had a charged ion, we should have a 

 still stronger field and still more condensation. The Con- 

 ducfion of Electricity through Gases gives us evidence of 

 such condensation, as the ions behave rather as if they were 

 clusters of molecules than simple molecules or atoms. It 

 may, however, be asked why is it, if the molecular doublets 

 are able to accelerate chemical actions, that the speed of 

 such reactions is not notably greater in an ionized gas than 

 in one which is not ionized ? The answer is that in any 

 ordinary type of ionization the number of charged ions is- 

 exceedingly small in comparison with the number of mole- 

 cules of a substance, even when this is present as the merest 

 trace. Take, for example, the case of water-vapour : if the 

 partial pressure of the vapour were only the millionth of an 

 atmosphere, there would still be about 2'8 x 10 13 molecules 

 of water-vapour per cubic centimetre. It would be ex- 

 ceptionally strong ionization by such an agent as Rontgen 

 rays to produce 10 10 ions per cubic centimetre, so that the- 

 molecules of water-vapour when this trace of water was 

 present would be about three thousand times the number of 

 ions. In cases where there are exceptionally large numbers 

 of ions present, as for example in the negative glow in a 

 discharge-tube, all kinds of chemical action seem to go on 

 with great facility. 



On the Number of Active Molecules which a Molecule of a 

 (liferent kind can hold in Combination. 



We shall denote one of the active molecules by B, the 

 molecules to which these are attached by A. We have to 

 consider in the first place whether A can hold even one of 

 the type B bound. From general Thermodynamical con- 

 siderations it is clear that the system AB will not be formed 

 in appreciable quantities unless the work required to separate 

 A and B when they are in combination is considerably larger 

 than R0, the energy corresponding to one degree of freedom 

 at the absolute temperature 6. If we regard the electric 

 field round the atoms as equivalent to those produced by 

 electrical doublets whose moments are respectively M, M',. 



