THE THERMAL DECOMPOSITION OF H₂0₂ VAPOUR
1. A convenient method for the preparation of small
quantities of chemically pure, very concentrated
hydrogen peroxide has been further developed.
2. The decomposition of hydrogen peroxide vapour
has been examined on various surfaces at pressures up
to 5 mms. at various temperatures in the range
18 - 110 °C. The appearance of both second and first
order characteristics on a silica surface is
attributed to a change in the surface action rather
than to a strong retardation of the decomposition by
water vapour.
3. Octa -decyl alcohol was found to give a very
stable surface and very reproducible results were
obtained in a silica vessel coated with this compound
Oxygen, nitroen, water vapour and carbon dioxide
were found to have no effect on the rate of
decomposition.
4. Films of cobalt salts were found to accelerate
the rate of decomposition but acetanilide and octadecyl alcohol gave rates which were of the same order
of magnitude as on the uncoated silica surface.
5. The second order decomposition was found to have
a negligible temperature coefficient but the first
order decomposition had a heat of activation of
approximately/
approximately 12 k.cals. per mole, both on a silica
surface and octa- d.ecyi alcohol.
6. - With high pressures of water vapour, periodic
variations in pressure were observed. A possible
explanation of this behaviour is discussed.
7. Since high pressures of oxygen and nitrogen
(400 mms.) have no effect on the rate, it is suggeste
that the rate of diffusion in the bulk of the vapour
has no effect on the rate of decomposition.
8. An attempt has been made to evaluate the absolute
velocity of reaction from an equation derived from the
theory of absolute reaction rates. The velocity so determined was found to be 4.4 x 10¹² molecules H₂0₂ cm⁻² sec⁻¹ at a temperature of 27.2 °C on an octa -decy
alcohol surface, in good agreement with the
experimental value of 6.9 x 10⁻¹² molecules H₂0₂ cm.⁻² sec.⁻¹
THE PHOTO -FORMATION OF H₂0₂
1. Zinc oxide, titanium dioxide and zinc sulphiac
nave been shown to adsorb dry oxygen on illumination
with visible light. This adsorption is. partially
reversible.
2. Aqueous suspensions of zinc oxide, titanium
dioxide and zinc sulphide produce an oxidising agent
when illuminated in presence of oxygen.
3. The oxidising agent produced, in the case of
inc oxide suspensions, has been shown to be hydrogen
eroxide.
4. Several mechanisms suggested to explain the
degrading action of photosensitive dyes on textiles
are discussed and their application to the activity
of the white pigments considered.
5. An activated form of oxygen, either an excited
molecule or an oxygen ion, is suggested as being formed.
.n the illumination of the white pigments in dry oxygen. This activated oxygen is considered to be an intermediate in the formation of hydrogen peroxide in
aqueous suspensions.
