It would take 8928.5714285714285714285714285714 hours for
.5 grams of mercury to evaporate completely at 68F degrees,
assuming an evaporative surface area of 1 square centimeter.
This is based on the volatility of mercury, which is the
measure of how quickly it evaporates, and is 0.056 mg/h.cm²,
or .056 milligrams per hour per square cm, at 68F or 20C:
"Given that the volatility of mercury at a temperature of
20°C is 0.056 mg/h.cm²"
From a document titled 'Code of Practice Mercury Housekeeping',
page 13, on the United Nations Environment Programme - Chemicals:
The chart just below this statement, in the link above,
indicates how mercury evaporates more quickly in proportion
to the increase in surface area exposed, so .5 grams in a
single globule won't evaporate nearly as fast as the same
amount dropped onto the floor and scattered into multiple
tiny globules. It illustrates how 1000 tiny droplets, vs
one droplet of equal volume, will increase both the
evaporative surface area and the rate of evaporation by
a factor of 10.
Now 68F = 20C, and 70F = 21.1111111C, which is a very small
increase in terms of the volatility of mercury, so this
increase in temperature would take only slightly less time.
I am unable to determine the exact difference since I was
unable to find a formula for the volatility of mercury at
the temperature of 21C. Such formulae are typically given
a standard format based on normal room temperature. Out of
8928 hours, I would guess it would take just a few hours
less to evaporate at 70F.
The change in the volatility of mercury is nicely illustrated
in the charts shown on page 3 of this PDF file, titled
'Release of Mercury From Broken Fluorescent Bulbs' from the
website of the State of New Jersey:
As you can see, there is no significant difference in
the volatility of mercury between 40F and 60F. At 85F,
however, you can see that the evaporation occurs almost
twice as quickly as it does from 40-60F.
I hope this satisfies your needs in asking the question,
as I sincerely doubt that a more accurate answer can be
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A user's guide on this topic is on skermit-ga's site, here:
Additional information may be found from an exploration of
the links resulting from the Google searches outlined below.
Searches done, via Google:
mercury "rate of evaporation"
"volatility of mercury" temperature