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Salt and Dehydration
Name: Mitchell
Status: student
Grade: 6-8
Location: CA
Country: N/A
Date: January 2007
Question:
I have been studying ancient Egypt and the mummification process. A
certain salt called natron was used but I cannot find out how it
actually dehydrated the body. How does any salt, such as Epsom,
table salt and baking soda dehydrate for example an apple. What is
the chemical process?
Replies:
Mitchell,
Instead of rehashing another web site, read this link:
http://en.wikipedia.org/wiki/Natron
To get a little more specific from what Wikipedia states, the
chemical process (it is not actually a reaction) of dehydration by a
salt is called hygroscopicity. Again, I will redirect you to Wikipedia :)
http://en.wikipedia.org/wiki/Hygroscopic
Matt Voss
Mitchell- try this on for size.
I think salts of almost any kind, if at high concentration in the water
solution,
kill most micro-organisms or greatly retard their growth.
So while the body is sitting there years in the dry desert,
not rotting because the germs are inhibited by a pile of excess salt
infusing into the tissues,
the only thing it can do is gradually dehydrate.
Some salts are "hygroscopic", meaning they pull water vapor from the
surroundings
and change their crystal structure to include it, or they turn into thick
salt slush.
As long as some solid salt still exists, the solution is saturated with a
fixed percentage of salt,
and it keeps trying to pull in more water and get dissolved.
After there is enough water added to completely dissolve the salt,
when more water actually dilutes the solution,
only then can the humidity start rising above the equilibrium humidity level
of this salt's saturated solution.
This saturation humidity can be anywhere from 5% to 70% humidity,
depending on which salt.
If a hygroscopic salt is in an enclosed chamber,
the chamber dries out to some low percentage relative humidity.
Eventually perhaps water vapor diffuses through all the wrappings and escapes
into the desert,
if the desert's average humidity is drier than the salt's saturation
humidity level.
But before that, this kind of salt would give the entombed body a head
start on drying out.
And afterwards it would act as protective water-absorbing capacity
in case some water seeps in during unusually wet periods.
I have not yet looked up what salts natron has and whether they are
hygroscopic.
There is a table of chemical desiccants in the CRC Handbook of Chemistry
and Physics.
Jim Swenson
Mitchell,
Natron is most likely a mixture of compounds based on sodium -recall
that the original name of sodium is natrium, chemical symbol "Na".
It is most likely composed mainly of sodium carbonate (Na2CO3) or
sodium hydroxide (NaOH). Both these compounds are hygroscopic, that
is, they absorb moisture. Sodium carbonate is known to form mono-,
hepta-, and deca- hydrates, that is, one molecule of sodium
carbonate can form a complex with 1, 7 or 10 molecules of water
respectively. This means that when water molecules come into contact
with moisture, these hydrates form and essentially extract the
moisture from the surrounding environment. Since cell activity, the
action of bacteria, enzymes and such is dependent on the presence of
water as a solvent, extracting the water from the cells effectively
slows down or stops these process and prevent decomposition. Thus,
the desiccated (dried) nature of mummies is what allows for the
preservation process.
Greg (Roberto Gregorius)
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