4 
DR. W. A. BONE AND MR. R. V, WHEELER ON THE COMBINATION OF 
We may now consider, a priori, the factors which may determine the velocity of 
an irreversible gaseous reaction of the type A+B = AB in a heterogeneous system. 
Regarding the matter from the kinetic standpoint, the observed rate of change will, 
in the absence of other disturbing factors, depend on (1) the actual rate of combination 
at the surface; (2) the rates at which A and B, respectively, diffuse inwards from the 
inert atmosphere outside on to the surface; and (3) the rate at which the product AB 
diffuses outwards. N ernst* has recently advanced a general theory of reactions in 
heterogeneous systems based on measurements of the rates of solution of salts in 
water, or of metals and such substances as magnesia, marble and metallic hydroxides 
in acids. He assumes that, for all practical purposes, the rate at which equilibrium 
is established at the limiting surface between the two phases (solid-liquid or solid-gas) 
is infinitely great compared with the rates of diffusion of the reacting substances on 
to, or of the reaction product away from, the surface. Hence the velocity observed 
in the system will depend not on the “ order ” of the reaction, but on the diffusion 
factors only. Our experiments have proved that this “ diffusion” theory is incapable 
of explaining the facts of the catalytic combination of hydrogen and oxygen. There 
are clearly other factors which have a determining influence on the course of events. 
Bodenstein’s Experiments. 
In the year 1899 M. BodensteinI published the results of experiments on the non¬ 
explosive combination of electrolytic gas during its passage through a glazed porcelain 
tube heated in a lead bath to various temperatures between 482° and 689°. The 
author was himself conscious of certain inherent sources of error in his experimental 
method, which influenced the results quite irregularly and often in a very annoying 
manner (“in oft reclit unliebsamer Weise”). In view of this admission it is difficult 
to say what is the precise significance of his work. Whilst fully recognising that he 
was dealing with a surface phenomenon entirely, Bodenstein concluded that it is 
impossible to deduce any mathematical expression for his results other than the 
equation for a reaction of the third order. This, of course, means that, notwith¬ 
standing the fact that the reaction was entirely confined to the layer of gas 
immediately in contact with the walls of the reaction vessel, its velocity was governed 
by its “order” in accordance with the law of mass action. We shall, however, have 
no difficulty in proving that this conclusion is wrong. 
* ‘Zeit. Phys. Chem.,’ 1904, vol. 47, p. 52. In applying the theory to the special case of catalytic gas 
reactions, Nernst remarks, “ Da diese Reaktionen wold ausschliesslich an der Grenzflache des Katalysators 
Abspielen, so wire! die Geschwindigkeit keineswegs durch den Meckanismus der betreffenden Reaktion, 
sondern wenn, was allerdings von vornherein nicht sicher ist, der Katalysator wahrend des Reaktions- 
verlaufes konstante Beschaffenheit behalt und zugleich mit praktisch unencUicher Geschwindigkeit die 
betreffenden Substanzen an der Grenzflache zur Reaktion bringt, auch hier lediglich durch die Diffusion 
der reagierenden Stoffe zum Katalysator bedingt werden,” p. 55. 
t ‘Zeit. Phys. Chem.,’ 1899, vol. 29, p. 665. 
