Re: [rete] Passevin

[Tom Ford <tomford@THESCIENCESOURCE.COM>]

But you can have it all!. Back up your one liter graduate or hydrometer jar
with a narrow piece of bright yellow construction paper and fill the
container with water to the brim. Having grown a copper sulfate crystal on
a string, hang it by the string against the side of the graduate just below
the water line. Make up water for evaporative and sampling losses can be
delicately added at the top. Expect this to look different every day of the
next school year (or most of it, you might get bored) as the density plume
from the crystal fills from the bottom, whence the diffusion is easily
viewed against the background. To take periodic data, use a finger-capped
piece of small bore tubing to extract small samples from different
locations and examine these with a simple LED-type of photometer over the
course of a very long time. Marvelous opportunity to make and interpret
graphs over that long time span. Just don't shake or stir. Works best if
the container can remain totally undisturbed (glass case in hallway?) for
the duration.

Tom Ford

At 10:12 AM 6/24/04, you wrote:
> For those who don't have red wine in the supply cabinet, you might tr=
> y sugar water or salt water with food coloring.  Your deparment head =
> won't look at you quite as funny when you ask for a signature for sug=
> ar!
>
> As a sort of reverse of this rapid change, you might try the opposite=
>  - put the heavier liquid at the bottom.  I filled the bottom half of=
>  a graduated cylinder with blue sugar water, then carefully add red w=
> ater on top.  (I used a tube so that I could slowly add the water rig=
> ht at thr top of the lower layer without splashing, dropping, stirrin=
> g, etc.  I was greatly surprised that it took WEEKS for the colors to=
>  do much mixing.  I also took apart a battery tester and added the li=
> ttle floating balls which floated in the purple region, slowly separa=
> ting as the fluids mixed. =20
>
> I can't remember now what inspired me to try this - if someone else h=
> ad suggested it, or if it was a variation on some other demo I saw, o=
> r if it was just a random thought.  Perhaps I should repeat the exper=
> iment and submit it to TPT in a short article.
>
> Tim F=20
>
>
> -----Original Message-----
> =46rom: Forum for Physics Educators on behalf of Brian Whatcott
> Sent: Wed 6/23/2004 6:07 PM
>
> >>A glass of red wine, full exactly up to the upper edge.
> >>A second glass similarly full of water. A sheet of paper is put jus=
> t on
> >>the surface, in contact with the edge and with water.
> >>
> >>Take the second glass in your right hand, maintain the paper sheet =
> in
> >>place with your left hand, and turn it over, while preventing the w=
> ater
> >>to flow outside the glass with the paper sheet. Put delicately the =
> turned
> >>over water glass on the first one, exactly edge against edge.
> >>
> >>Then, very, very slowly, pull the paper sheet towards you in order =
> to
> >>remove it completely.
> >>
> >>Then, very progressively, you see the diffusion of the red wine tow=
> ards
> >>the upper glass, while it is replaced by water in the lower one. Af=
> ter
> >>some minutes, the upper glass is full of wine, and the lower is qui=
> te
> >>clear ! It is really amazing.
> >>
> >>P. Lauginie