9 
DR. W. A. BONE AND MR. R. V. WHEELER ON THE COMBINATION OF 
( b) The subsequent combinations of (l) four arsenic atoms forming the complex As*, 
and (2) two hydrogen atoms forming H 2 , both combinations taking place 
with relatively infinite velocities. 
The recent determinations of the velocity of the decomposition of ammonia in 
porcelain vessels at high temperatures by Dr. Perman and Mr. Atkinson* indicate 
that it is always proportional to the first power of the ammonia concentration. The 
authors concluded that the decomposition “ is monomolecular, proceeding according to 
the equation NH 3 = N + 3H ; the union of the atoms to form molecules is probably so 
quick that it can be neglected when compared with the rate of decomposition of the 
ammonia molecule” (p. 116). 
It may, however, be seriously questioned whether the above assumptions are 
admissible: whether, in such cases, we are dealing with a chemical change in a 
homogeneous system to which the principle of mass action can be applied. 
In discussing the velocities of gaseous reactions, the catalytic influence of the 
heated surface to which the gases are exposed, i.e., the walls of the containing vessel, 
or any solid material with which it may be packed for the purpose of accelerating the 
reaction, has hitherto not received the attention it deserves. Many workers have 
investigated the combination of gases in glass vessels at elevated temperatures, and 
it is generally agreed that, in a large number of cases, the chemical change is 
mainly, if not entirely, confined to the layer of gas immediately in contact with the 
surface. We may here recall the many independent attempts of Van’t Hoff and 
Victor Meyer to measure the velocity of the interaction of hydrogen and oxygen in 
glass bulbs, at temperatures below the ignition point. Their efforts were, however, 
frustrated by the controlling influence of the “ surface factor.” It would appear, 
therefore, that whatever may be the mechanism of the “ surface action," the gas 
actually lying on the surface is in a different condition from the main body of the gas, 
and that this condition is more favourable to chemical interchanges. The system is, 
therefore, not homogeneous, and the law of mass action does not generally apply to it. 
The power possessed by platinum and certain other metals of inducing the 
combination of hydrogen and oxygen at low temperatures engaged the attention 
of many eminent investigators during the early part of last century. In 1817 
Sir H. Davy f di scovered that a warm spiral of platinum wire will bring about the 
ignition of hydrogen, and in the next year ErmanJ found that electrolytic gas may 
be fired by such a spiral warmed to 50° only. The subject was, however, first 
systematically investigated by Dulong and Thenard§ and, independently, by 
Dobereiner || in the year 1823. Dulong and Tiienard found that the activity of 
* ‘Roy. Soc. Proc.,’ 1904, vol. 74, p. 110. 
t ‘Phil. Trans.,’ vol. 107, 1817, p. 77; ‘Quart. Journ. of Science,’ vol. V., ISIS, p. 128. 
J ‘ Abhandlungen der Akademie der Wissenschaften in Berlin fur 1818-1819/ p. 368. 
§ ‘Ann. Chim. Phys.,’ vol. 23, 440; vol. 24, 380. 
|| ‘ Schw.,’ 34, 91 ; 38, 321; 39, 159; 42, 60; 63, 465. 
