[meteorite-list] fukang (the neverending thread)/what countryisthe hardes...

[MexicoDoug at aol.com]

Hi Marcin and Matteo - Tropical refers to latitude, and humidity refers to  
weather.  They are independent.  0 humidity exists only in outer  space...or on 
the Moon, etc...even the driest deserts are in the 10% relative  humidity 
range.

BUT!  Air doesn't get more than about 4% absolute  humidity anywhere, I 
recall.  That's the most vapor than can actually be  put into the air 
percentage-wise.  So, in a sweltering hot place, with a  disturbing 62% RELATIVE humidity, 
there is less than 2.5% absolute humidity, but  if you cool it down it rains.  
So in the tropics you get lots of rain in  the late afternoon - and rapid 
fluctuation in temperature cause condensation and  precipitations.  Matteo didn't 
say relative humidity so if we willingly  generously gave him the benefit of 
the doubt, we can assume he meant absolute or  specific humidity.  Venice may 
be all wet, but so it Antarctica, in a  sense.
 
Arizona is does have higher temperatures, but it is not any more tropical  
that the frequently brutal temperatures of Death Valley, California (which does  
team with life)... and the driest places on Earth include the polar desert  
"Valley of the Dead" (Taylor Valley) of Antarctica and the Gobi desert, the  
later having average temperatures below zero!  One factor additionally to  
consider in a desert is the radiative effect for an iron meteorite being baked  in 
the sun with a dark magnetite layer ... it gets hot, and so does the air  
immediately around it!
 
When we heat things up to dry them out...it is not principally the "heat"  
doing the drying on the object.  It is the elevated temperature of the air  
around the object sucking the water out of the object because of the equilibrium  
being pushed increase the total amount of water the air holds, and the air  
"attracts" the water just like a vacuum would...
 
Add to that, rusting happens what, twice as fast for every 10 degrees C  
increase in temperature?...and it is easier to relate to the comments on some of  
the stability of Russian irons...

Relative humidity is not easily comparable from one location to another  
without considering the temperature.  You compare them in a Mollier Diagram  and 
answer almost any humidity-saturation-water concentration question looking  at 
one.  The warm the ambient temperature, the more water vapor that the  air 
holds until it gets saturated.  30% relative humidity IS less water in  a colder 
place than a warmer place that has the same 30% relative  humidity.

Does this make sense?  Part is intuition but part is  somewhat 
counterintuitive...but to understand the crux of what happens to  preserve meteorites 
exposed to the air or even soil, these processes are the  ones to mull for the 
environments.

Saludos, Doug


1/6/2006  9:20:33 A.M. CST Matteo writes:

>not sure from me....a person live in  Arizona have a "
>little " difference on humidity from one live  in
>Venice....

Matteo


1/6/2006 7:56:57 A.M. CST, Marcin  writes:

> Right, I have many pieces of Seymchan and never seen  a
> trace of rust. And Russia is not a tropical land where
> the  umidity its near the 0. The same for Esquel and
> Imilac, super stable  pallasite.
> Matteo

Matteo, how in Tropical climate humidity can be  0 ?