as not
affected by plates after fifty hours. I am inclined to refer the effect to
carbonic oxide present in the gas, but have not had time to verify the
suspicion. The power of the plates was not destroyed (640. 646.).

655. Such are the general facts of these remarkable interferences. Whether
the effect produced by such small quantities of certain gases depends upon
any direct action which they may exert upon the particles of oxygen and
hydrogen, by which the latter are rendered less inclined to combine, or
whether it depends upon their modifying the action of the plate temporarily
(for they produce no real change on it), by investing it through the agency
of a stronger attraction than that of the hydrogen, or otherwise, remains
to be decided by more extended experiments.

* * * * *

656. The theory of action which I have given for the original phenomena
appears to me quite sufficient to account for all the effects by reference
to known properties, and dispenses with the assumption of any new power of
matter. I have pursued this subject at some length, as one of great
consequence, because I am convinced that the superficial actions of matter,
whether between two bodies, or of one piece of the same body, and the
actions of particles not directly or strongly in combination, are becoming
daily more and more important to our theories of chemical as well as
mechanical philosophy[A]. In all ordinary cases of combustion it is evident
that an action of the kind considered, occurring upon the surface of the
carbon in the fire, and also in the bright part of a flame, must have great
influence over the combinations there taking place.

[A] As a curious illustration of the influence of mechanical forces
over chemical affinity, I will quote the refusal of certain substances
to effloresce when their surfaces are perfect, which yield immediately
upon the surface being broken, If crystals of carbonate of soda, or
phosphate of soda, or sulphate of soda, having no part of their
surfaces broken, be preserved from external violence, they will not
effloresce. I have thus retained crystals of carbonate of soda
perfectly transparent and unchanged from September 1827 to January
1833; and crystals of sulphate of soda from May 1832 to the present
time, November 1833. If any part of the surface were scratched or
broken, then efflorescence began at that part, and covered the whole.
The cry