Subject: How gravitation effects molecule distribution in solutions

Hi,

Surely I am mad enough, but I am not a scientist so I really need to hear your 
opinion.

If I put small amount of heavy water into a cup of normal water – two things 
can happen: 

a) Heavy water molecules can spread uniformly 
b) Due to gravitation force, there will be slightly more heavy water molecules 
near the bottom of the cup than near the top (difference probably not 
measurable) 

If the answer is a) then read no further.

Instead of putting heavy water I could dissolve some sugar into the water.  
Again, will sugar molecules spread uniformly or not? If the answer is ‘not’ 
then read no further.

Is there any molecule bigger than water molecule that, when dissolved in 
water, will make measurable difference in concentration near the top and the 
bottom of water cup due to gravitation force (or, maybe, strong centrifugal 
force)?

If such molecule exist then I have a problem… Imagine a small closed box fully 
filled with such water solution. The top and bottom sides of the box are semi-
permeable membranes (permits water molecules but not our big molecule). We put 
the box into the water. Due to difference in concentration at the top and at 
the bottom of the box there will be difference in osmotic pressure (?) that 
will cause perpetual motion of the water (?!).  You see now why I am mad ;).

Re: How gravitation effects molecule distribution in solutions