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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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