Abstract
The outcome of these low pressure investigations,
in so far as chemistry was concerned, was to emphasise
the importance of interfaces on the progress of gas
reactions. Thus the Van't Hoff period in gas
kinetics was succeeded by a period in which the
differentiation between homogeneous and heterogeneous
reactions was established by careful experimental work. Another impetus to the study of gas reactions
was given hy the acute controversy on the origin of
the energy of activation in homogeneous reactions resulting in the rise and fall of the radiation hypothesis of activation. Similarly, the discussion
of the validity of the Stark-Einstein law of
photochemical equivalence played a not inconsiderable
part in laying the foundation for the theory of
thermal chain reactions. How this came about
will be shown in the sequel.
It may be stated at the outset that the
reaction between phosphorus and oxygen is a chain
reaction. The recognition of this fact only dates
from 1927. However, the amount of attention which
this reaction has attracted during the last hundred
years has led to the accumulation of a very extensive
literature relating to the subject. No attempt
will be made below to survey or discuss this
literature except in so far as it may refer to or
supplement experiments at low pressures. Nor will
any treatment be given concerning the origin or
mechanism of the production of the green glow during
the oxidation. Instead, the subject will be considered from the point of view of chain reactions.
The literature pertaining to the subject of
chain reactions has grown considerably during the
past few years, but since so many of the reactions
studied bear a formal and sometimes a very close
resemblance to the phenomena exhibited by the
oxidation of phosphorus vapour it will be necessary
to pay attention to the subject of chain reactions
in general.
This essay is divided into seven sections:
Section 1. The general theory of thermal chain
reactions;
Section 2. Experimental evidence supporting the
theory;
Section 3. The quantitative theory of the oxidation
of phosphorus at low pressures;
Section 4. The effect of foreign gases of the lower
critical explosion pressures of P₄-O₂
mixtures. - Experimental results and
discussion;
Section 5. A sensitive direct reading mercury
manometer;
Section 6. The combination of phosphorus and oxygen
at low pressures in presence of platinum
and tungsten. Results and discussion;
Section 7. Discussion of the P₄-O₂ reaction in
general, reviewed in the light of the
results described in Sections 4-6.
