A vacuum will hold up a column of water about 10
meters, so how does water get to the top of very
tall trees?
Peter

In article ,
Peter Jason wrote:
A vacuum will hold up a column of water about 10
meters, so how does water get to the top of very
tall trees?
Peter

The water isn't held up by vacuum (actually the external air pressure, not
the vacuum per se) but by capillary action in series of very fine tubes.
The cohesion of the water molecules to each other is what keeps the
water up and rising as water evaporates from the periphery of the tree.

N.B. This is why you cut off the bottom of flower stems before you put
the bouquet in water.

On 31 Aug 2012 11:37:21 GMT,
wrote:

In article ,
Peter Jason wrote:
A vacuum will hold up a column of water about 10
meters, so how does water get to the top of very
tall trees?
Peter

The water isn't held up by vacuum (actually the external air pressure, not
the vacuum per se) but by capillary action in series of very fine tubes.
The cohesion of the water molecules to each other is what keeps the
water up and rising as water evaporates from the periphery of the tree.

N.B. This is why you cut off the bottom of flower stems before you put
the bouquet in water.

Thank you. I was also wondering why water
evaporates more quickly from cotton (cellulosic)
materials faster than from polyester, nylon, glass
wool, and rubber foam etc. Indeed the difference
is quite marked.

As an experiment I put a petri dish on to a
balance and in its center weighed a 1 gram piece
of various substrates such as filter paper, cotton
wool, cotton pajamas, nylon rope, glass wick,
canvas, orlon and the like. In the center of
these materials I placed 1gm of distilled water.
In all cases the cellulose materials dried much
faster than any other. Almost twice as fast.

Strange, because this is the opposite I expected
given the OH groups on the cellulose and their
likely hood of their forming H-bonds with the
water and so retaining it. EG a nylon shirt will
dry faster than a cotton one, or so it seems
though evidently the nylon article will contain
less water when wet.

In article ,
Peter Jason wrote:

Thank you. I was also wondering why water
evaporates more quickly from cotton (cellulosic)
materials faster than from polyester, nylon, glass
wool, and rubber foam etc. Indeed the difference
is quite marked.

As an experiment I put a petri dish on to a
balance and in its center weighed a 1 gram piece
of various substrates such as filter paper, cotton
wool, cotton pajamas, nylon rope, glass wick,
canvas, orlon and the like. In the center of
these materials I placed 1gm of distilled water.
In all cases the cellulose materials dried much
faster than any other. Almost twice as fast.

Strange, because this is the opposite I expected
given the OH groups on the cellulose and their
likely hood of their forming H-bonds with the
water and so retaining it. EG a nylon shirt will
dry faster than a cotton one, or so it seems
though evidently the nylon article will contain
less water when wet.

I suggest you look at your samples both dry and wet with varying amounts
of water under a low power microscope. Most of the fibers you list
do not absorb water, so the limited amount of water you used just sits
between the threads. THis causes a great deal less water surface to be
exposed to air than if it is absorbed into cotton threads.

Note that the diameter of the fibers of these materials and the tightness
of the weave or twist are important factors and should be controlled for,
as is the thickness or surface area to volume ratio of the samples. Also,
what was your endpoint for determining that the sample was dry again?
It should be the sample returning to a weight of 1 gram, and you should
control for air motion, temperature and humidity.

A nylon shirt will dry faster than a cotton one because it holds less
water after being washed. You might want to experiment with weighing
samples of various materials before and after being immersed in water
and wrung, squeezed or spun out.

You might be interested to examine wool fibers carefully both wet and dry.
Like hair, they are covered with overlapping scales that remain from
the cells they are composed of. Wool fibers absorb water and swell,
trapping it. This explains why wool fabric is slow to dry and why it
is unique in textile fibers for making garments that are warm even when
they are wet.

See if your library has any books on textiles and textile fibers.
I've got a book I picked up at a rummage sale that is the text for
a community college course in textile science, and the description
of how synthetic and natural fibers are prepared, spun and woven is
very interesting. Developments in the past few decades have made some
surprising changes from the straightforward mechanization of techniques
that go back for millennia. For example, weft fibers can be spun into
thread by air currents as the fabric is woven in sealed looms, and
non-woven textiles with a wide range of properties are becoming more
common for both traditional and innovative uses.

We've kind of gotten away from botany here. Good luck with your projects!

On 1 Sep 2012 17:08:10 GMT,
wrote:

In article ,
Peter Jason wrote:

Thank you. I was also wondering why water
evaporates more quickly from cotton (cellulosic)
materials faster than from polyester, nylon, glass
wool, and rubber foam etc. Indeed the difference
is quite marked.

As an experiment I put a petri dish on to a
balance and in its center weighed a 1 gram piece
of various substrates such as filter paper, cotton
wool, cotton pajamas, nylon rope, glass wick,
canvas, orlon and the like. In the center of
these materials I placed 1gm of distilled water.
In all cases the cellulose materials dried much
faster than any other. Almost twice as fast.

Strange, because this is the opposite I expected
given the OH groups on the cellulose and their
likely hood of their forming H-bonds with the
water and so retaining it. EG a nylon shirt will
dry faster than a cotton one, or so it seems
though evidently the nylon article will contain
less water when wet.

I suggest you look at your samples both dry and wet with varying amounts
of water under a low power microscope. Most of the fibers you list
do not absorb water, so the limited amount of water you used just sits
between the threads. THis causes a great deal less water surface to be
exposed to air than if it is absorbed into cotton threads.

Note that the diameter of the fibers of these materials and the tightness
of the weave or twist are important factors and should be controlled for,
as is the thickness or surface area to volume ratio of the samples. Also,
what was your endpoint for determining that the sample was dry again?
It should be the sample returning to a weight of 1 gram, and you should
control for air motion, temperature and humidity.

The experiment was in two parts, with a large
undefined amount of water per substrate, and the
second with a substrate/water ratio 1:1.

The temperature varied between 12 - 14degC, and
the humidity in a closed room was 60 - 70%RH.

The sample was tared and the water added. The
scales indicated the water loss over some hours,
and the results, to date, are here. Note the
much faster loss of water from the cotton
(cellulosic) fabrics. This is opposite to what I
expected.
http://img856.imageshack.us/img856/2070/dryingtimes.jpg


A nylon shirt will dry faster than a cotton one because it holds less
water after being washed. You might want to experiment with weighing
samples of various materials before and after being immersed in water
and wrung, squeezed or spun out.

You might be interested to examine wool fibers carefully both wet and dry.
Like hair, they are covered with overlapping scales that remain from
the cells they are composed of. Wool fibers absorb water and swell,
trapping it. This explains why wool fabric is slow to dry and why it
is unique in textile fibers for making garments that are warm even when
they are wet.

See if your library has any books on textiles and textile fibers.
I've got a book I picked up at a rummage sale that is the text for
a community college course in textile science, and the description
of how synthetic and natural fibers are prepared, spun and woven is
very interesting. Developments in the past few decades have made some
surprising changes from the straightforward mechanization of techniques
that go back for millennia. For example, weft fibers can be spun into
thread by air currents as the fabric is woven in sealed looms, and
non-woven textiles with a wide range of properties are becoming more
common for both traditional and innovative uses.

We've kind of gotten away from botany here. Good luck with your projects!