498 REPORTS ON THE STATE OF SCIENCE. 



of salts in water, or of such substances as magnesia in acids, ignores 

 (in the case of surface combustion) the possible ' activation ' of the 

 gases by the surface, and contends that the velocity of surface com- 

 bustion is governed by diffusion factors only. Thus he has written : — 



' Da diese Reaktionen wold ausschliesslich an der Grenzflache des 

 Katalysate?i abspielen, so wird die Geschwindigkeit keineswegs durcli den 

 Mechanismus der betreffenden Reaktion, sondern wenn, was allerdings 

 von vornherein nicht sicher ist, der Katalysaten wahrend des Reaktions- 

 verlaufes konstante Beschaffenheit behdlt und zugleich mil praktisch 

 unendlicher Geschwindigkeit die betreffenden Substanzen an der Grenz- 

 flache zur Reaktion bringt, auch hier lediglich durch die Diffusion der 

 reagierenden Stoffe zum Katalysaten bedingt werden.' x 



Bodenstein, 2 in an entirely inconclusive series of experiments on the 

 combination of hydrogen and oxygen in contact with platinum at the 

 ordinary temperature, attempted to provide an experimental basis for 

 the above theory, but it has been recently completely disproved by 

 the researches of the writer and his pupils (R. V. Wheeler, G. W. 

 Andrew, A. Forshaw, and H. Hartley), a first instalment only of 

 which has so far been published. 3 The following is a brief resume 

 of the principal results of these researches: — ■ 



At an early stage of the research it became manifest that, in order to 

 avoid errors inherent in a too restricted view of the phenomena, the 

 action of a considerable variety of surfaces must be studied, including 



(1) such ordinarily non-oxidisable metals as gold, silver, and platinum, 



(2) oxidisable metals, such as copper and nickel, (3) easily reducible 

 oxides, as well as (4) non-reducible oxides of both basic and acidic 

 character. Although the investigation has revealed certain minor 

 differences between the action of the various surfaces, the results as a 

 whole leave no room for doubt but that the catalytic combustion depends 

 primarily upon . the condensation or absorption of one or other (and 

 possibly both) of the reacting gases by the surface, whereby they are 

 rendered ' active.' Any chemical explanation — such, for instance, as 

 the supposition of a rapidly alternating series of oxidations and reduc- 

 tions of the catalysing surface — is inconsistent with the numerous 

 velocity measurements made during the research. Equally certain is it 

 that the rate of combustion is governed, not by diffusion factors, as 

 Nernst has supposed, but by the rate of ' activation ' of one of the 

 reacting gases (and usually of the combustible gas) by the surface. 



The catalysing power of a new surface at a given temperature usually 

 increases up to a steady maximum when successive charges of the re- 

 acting gases, mixed in their combining ratios, are circulated over it ; 

 after the attainment of this steady condition, the rate of combination is 

 always directly proportional to the pressure, provided that the gases are 

 present in their ' combining ratios and the product of combustion is 

 rapidly removed from the sphere of action. Where, however, one or 

 other of the reacting gases is present in excess, the rate of combustion is 

 m nearly all cases proportional to the partial presence of the combustible 



1 Zeit, phys. Chan., 1904, 47, 55. 2 Ibid., 1903, 46, 725. 



s ' The Combination of Hydrogen and Oxygen in Contact with Hot Surfaces,' 

 Bone and Wheeler, Phil. Trans., 1906, A. 206, 1. 



