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The "Dude" wrote
>> Therefore, since the reaction takes place on the molecular level, there is
>> NO transfer of CO2 within the body of the granule, except via microscopic
>> holes in the granule itself. Once a molecule of CO2 has reacted with a
>> molecule of CaOH2 it becomes, once again, CaCO3, the Hydrogen atom is
>> driven off, where is combines with O2 and becomes water vapor once again.
Rich wrote
>So you mean that once binding sites on the surface of the particle are
>used up, no more become available? Then why does the color indicator
>change back to whit overnight - is it purely a temp thing? (i.e., if I
>heated it back up it would go purple again?)
The following is quoted from a manual that is produced for anesthesia
technicians by the makers of Sodasorb.
"COLOUR REVERSION
Color reversion is the phrase used to describe the reversion of
exhausted Sodasorb absorbent from purple to white when allowed to sit idle
for a few hours or more. In the past, the term regeneration (italic) of
soda lime has been incorrectly used to describe this process.
The color reversion is the result of subsurface calcium hydroxide
regenerating active hydroxide at the surface of the granule. This alters
the pH of the surface and, consequently, causes the indicator dye to revert
back to white, even though the Sodasorb my be near exhaustion.
Soda lime does not regenerate. Instead, there has been a reversion
of the indicator dye from purple to white. Although there may be some
additional carbon dioxide uptake due to the migration of these hydroxides,
the absorptive capacity of soda lime, perviously saturated with co2, is
minimal and should not be relied upon, even if the color of the granules has
reverted back to white.
It is important, therefore, for operating room personnel to
determine how much absorptive capacity is left in Sodasorb absorbaent
immediately at the end of a surgical procedure. Visual inspection at the
end of the rocedure will yeild an approxiamte estimate of the remaining
absorptive capacity. If it is purple a aquarte fo the way down, the
Sodasorb is exhaused by approximately 25%, half way down equials
approximately 50%, and so on."
Bill Brooks
PS Barrie and I have used the procedure mentioned in the last paragraph to
evaluate the sofnolime in our breather, we have found this to be a
relatively accurate method of determining the remaining duration in the
scrubber. Our scrubber is linear flow, seems to have a relatively flat
active zone and is made of a clear plastic material and is thus ideal for
this kind of monitoring.
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