202 PHENOMENA, ATOMS, AND MOLECULES 



Below this pressure the decrease in the heat loss is due to the temperature 

 discontinuity, first observed by Smoluchowski. The theory of this effect is 

 developed for the case of small wires at very high temperatures and the 

 results are found to be in good agreement with the experiments. 



6. The normal heat conductivity is separated from the abnormal effect 

 due to dissociation, and a table is prepared (Table III) giving the heat 

 carried from the wire by the dissociation, at various temperatures and 

 pressures. With nitrogen there is no abnormal increase in heat loss at high 

 temperatures. 



7. The following theory of the phenomena occurring in and around the 

 wire is proposed : 



The dissociation of the hydrogen does not occur in the space around the 

 wire, nor by the impact of molecules against its surface, but takes place 

 only among the hydrogen molecules which have been absorbed (dissolved ?) 

 by the metal of the wire. Within the metal the reaction occurs so rapidly 

 that equilibrium may be assumed to prevail at all times. 



The equilibrium constant within the metal may, however, be very 

 different from that in the gas phase. 



It is assumed that there is no "adsorption film" on the surface of the 

 wire through which the hydrogen has to diffuse, but that the absorption 

 takes place by the collision of the molecules (or atoms) against the surface 

 of the wire. A certain proportion of the molecules striking the surface 

 may be reflected without absorption. Thus, of all the hydrogen molecules 

 striking against the surface, we assume that a certain fraction aa is ab- 

 sorbed, while the fraction i — a2 is reflected. Similarly, of all the hydrogen 

 atoms striking the surface, the fraction ai is absorbed. 



In general, the partial pressures of atomic hydrogen in the gas immedi- 

 ately surrounding the wire will not be that corresponding to the equilibrium 

 at the temperature of the wire. The difference between these two partial 

 pressures may be looked upon as a "drop in concentration" at the surface 

 of the wire strictly analogous to Smoluchowski's "temperature drop" in 

 the case of heat conduction and to Kundt and Warburg's "slip" in the case 

 of experiments on the viscosity of gases. 



The partial pressure of atomic hydrogen immediately around the wire 

 depends on : ist, the rate at which atomic hydrogen escapes from the wire ; 

 2nd, the rate at which atomic hydrogen is absorbed by the wire ; and 3rd, 

 the rate at which it can diffuse away from the wire. 



8. From the viewpoint of this theory it has been possible, by thermo- 

 dynamical reasoning, to develop a quantitative theory by which the dis- 

 sociation constant K (in the gas phase) may be calculated in terms of Wd 

 the heat carried from the filament by dissociation ; qi the heat of reaction ; 

 D the diffusion coefiicient, and the two coefficients aj and a2. 



