PHILOSOPHICAL TRANSACTIONS. 
T. The Combination of Hydrogen and Oxygen in Contact with Hot 
Surfaces. 
By William Arthur Bone, Ph.D., D.Sc., F.R.S., late Bishop Berkeley Fellow 
of Owens College, Manchester, and Fellow of Victoria University, and 
Richard Yernon Wheeler, B.Sc., Dalton Scholar and 
Felloiv of Manchester University. 
Received November 14,—Read December 7, 1905. 
A large number of observations on the rates of chemical reactions in homogeneous 
systems, e.g., in solutions, has proved that the velocity of a given reaction is 
determined by its order-in accordance with the principle of mass action. It has been 
frequently assumed that the velocities of gaseous reactions are governed by the same 
law, although the few measurements which have been so far made hardly justify the 
assumption. Take, for example, the decomposition of arsine, the velocity of which 
was determined by enclosing the gas, at atmospheric pressure, in a glass bulb 
maintained at 310° and recording the pressure at the end of successive time 
intervals. # The results showed that the velocity of decomposition is directly 
proportional to the concentration of the arsine. On the assumption that the rate 
of change was governed by the law of mass action, it was concluded that the 
decomposition was a monomolecular one. But it is known that at temperatures 
below about 1000° the vapour of arsenic consists of tetratomic molecules, and, 
therefore, the equation for the decomposition of arsine at 310° must be written 
4AsH 3 = As 4 + 6H 2 . 
If so, then assuming that the decomposition takes place in a homogeneous system, its 
velocity should, according to theory, be proportional to the fourth power of the arsine 
concentration, and not to the first power as the experiment proves it to be. The 
discrepancy here indicated has been explained by the further assumption that the 
reaction really proceeds in stages, as follows :— 
(a) The monomolecular decomposition of arsine at finite velocity 
ASH 3 = As + 3H ; 
* D. M. KooiJ, ‘Zeit. Phys. Chem.,’ 1892, vol. 12, p. 155; J. H. Van ’t Hoff, ‘Studies in Chemical 
Dynamics’ (1896), p. 2. 
VOL. CCVI.—A 402, R 
29.5.06 
