Naked Science Forum

Life Sciences => Physiology & Medicine => Topic started by: paul.fr on 27/09/2007 13:34:30

Title: osmosis or not, i just don't know!
Post by: paul.fr on 27/09/2007 13:34:30

In another topic, the discussion was "why do your fingers wrinkle in the bath". Now i know this also happens when swimming in the sea. This lead me to an experiment with a baffling result.

Knowing that your fingers wrinkle in the salty sea water, i got  two bowls, filled one with warm water and the other with a saturated salt solution, and place one hand in each. After 30 minuites i took my hands out of the bowls. The hand in the warm water was, as expected wrinkly. Yet the hand that had been in the saturated salt water solution was wrinkle free!

what is going on?

Title: osmosis or not, i just don't know!
Post by: dkv on 27/09/2007 17:30:55

Simple. Salt water was not absorbed by the skin.

Title: osmosis or not, i just don't know!
Post by: Andrew K Fletcher on 27/09/2007 21:08:42

Not quite as simple as that. Osmosis predicts water being draw over a semipermiable membrane this has not happened why is this? I think this is the question being asked

Title: osmosis or not, i just don't know!
Post by: dkv on 27/09/2007 21:13:34

Salt water doesnt get absorbed by the skin readily.
Whereas the fresh water gets absorbed.
The granularity of salt water is greater.
Greater the granularity more difficult it is to penetrate the cell membrane.

Title: osmosis or not, i just don't know!
Post by: kdlynn on 27/09/2007 21:45:14

paul were the water temperatures the same?

Title: osmosis or not, i just don't know!
Post by: paul.fr on 28/09/2007 12:08:02

yes they were, kadie.

simply put. swimming in the sea (sea contains salt) gives you wrinkly fingers, yet when i put my hand in a saturated salt solution there were no wrinkles. why the difference?

Title: osmosis or not, i just don't know!
Post by: Carol-A on 28/09/2007 16:28:49

The sea is not saturated with salt though... perhaps thats the difference.

Title: osmosis or not, i just don't know!
Post by: WylieE on 28/09/2007 18:41:43

Hey Paul,

 The bowl solution result makes sense, the swimming one is odd.  Maybe you are swimming in an area near a river or other type of freshwater run off?  I often swim in salt water and can never remember my hands being wrinkled.  While swimming in a lake will wrinkle them fairly rapidly.  Perhaps the area you are swimming in is near a river or some other freshwater run off?  If this were the case the sea water would be diluted and salt concentration might be low enough to allow wrinkling. 

The osmolarity of sea water is from 2000mOsm to 2500mOsm.   That of your blood is 300mOsm- so, you "shouldn't" wrinkle in sea water- but maybe you are just really an old salt.
 [;D]
Colleen

Title: osmosis or not, i just don't know!
Post by: MayoFlyFarmer on 28/09/2007 19:57:42

Quote from: dkv on 27/09/2007 21:13:34

Salt water doesnt get absorbed by the skin readily.
Whereas the fresh water gets absorbed.
The granularity of salt water is greater.
Greater the granularity more difficult it is to penetrate the cell membrane.

salt should disolve in water.  there is no property that i know of called "granularity" of a liquid or a solution.