64 1.S.C. Proceedings of the Ninth [N.S., XVIII, 
Farmer (Jour. Chem. Soc. 1920, 117, 1603, 1432) has re- 
; cently shown that the velocity of decomposi- 
n chemical tion of high explosives becomes greater in pre- 
change will either gence of another explosive which is more 
pelennied a ed ot readily decomposed s far our experi- 
the same nature. ments go we are inclined to the view that 
one 
or induce another chemical change of the same nature. 
eing occupied so far with the question of acceleration 
and retardation of the velocity of chemical reactions, it would 
not be out of place to say a few words 
about the velocity itself. Within the last 
few years a great deal of theoretical work 
in this direction has been done notably by Perrin and Lewis. 
In a recent article (Ann. Phys. 1919 (9), 11, 5) Perrin shows 
that Arrhenius’ equation for reaction velocity and temperature 
Se can be derived from the Planck or Wien 
Meurer a ae radiation law on the assumption that the 
cal changes. chemical action depends on the absorption 
a nearly monochromatic radiation. In 
other words, these investigators postulate that radiation is 
the entire Motif of all chemical reactions, as well as of radio 
Mechanism of che- 
mical change. 
ture by exposing it to tropical sunlight even in absence of 
acids, and the inversion of cane sugar in the presence of 
hydrochloric acid is markedly accelerated by sunlight (com- 
pare Dhar Zeit. Anorg. Chem., 1920 
It should now be emphasised that there is no fundamental 
difference between the mechanism of photochemical and ther- 
mal reactions. Ina photochemical reaction the radiating body 
is not in thermal equilibrium with the reacting substance as it 
is in a thermal reaction, and the distribution of energy amongst 
the different frequencies does not necessarily follow Plancks 
distribution law. 
Poi pti 5 15 b ys 
