Acetic Acid - 31-8-2011 at 00:12
Whenever I do most reactions, I see these swirls in the reaction vessel. I don't know how to describe them, but you can clearly see them when you
dilute something with water, particularly sulfuric acid. I can even see them when looking at carbonated drinks or seltzer water. What causes these
"swirls"?
hissingnoise - 31-8-2011 at 00:55
Those 'swirls' are seen when liquids of differing density mix together.
Sulphuric acid is denser than water and refracts light to a greater degree.
Acetic Acid - 31-8-2011 at 00:57
Great explanation, thanks!
hissingnoise - 31-8-2011 at 01:06
The same thing is seen when cold and warm air mix.
And it's responsible for the 'mirage-effect' . . .
Acetic Acid - 31-8-2011 at 01:10
On a road on a hot day. Yes...
Arthur Dent - 31-8-2011 at 03:45
I remember seeing these cool-looking swirls when synthetizing methyl trichloride. As the acetone was slowly dripping drop per drop in the sodium
hypochlorite stirred gently with a stubby stirbar. At first, it was hardly noticeable, just two liquids with different densities, then it slowly
turned slightly turbid, and then woosh! In the space of one second, the entire flask became completely clouded, and turned from bright yellow to a
very light meringue beige.
The swirls were of course "amplified" by the stirbar and the vortex went right down to the bottom of the flask. The image isn't doing justice to the
swirl because it was much more clearly visible than that.
You can see the whole experiment here: http://www.sciencemadness.org/talk/viewthread.php?tid=9212&a...
Robert
Endimion17 - 31-8-2011 at 07:06
That phenomenon is especially visible on thin layers. For example, if you spill a concentrated solution of salt on a wet floor, and look in the light
that is reflected from lets say a lightbulb, you'll see them quite nice on the border of two liquids. Sometimes they seem to pulsate.
I always thought they are a nice example of fractal-like motions that are too weak to cause bigger swirls, and so they dissapear in the chaos of the
particles. We just happen to be of this size to be in the similar range, so we see them quite nicely.
unionised - 31-8-2011 at 13:06
You might find this interesting
http://en.wikipedia.org/wiki/Schlieren
Mr. Wizard - 1-9-2011 at 10:55
On the subject of Schlieren methods of seeing density and diffraction by means of parallel light being brought to a focus by lens, I discovered a
method by which you can see heat from your hand or from a warm breath.
I have never seen it described anywhere else, but it's very simple. I take my 6" old Edmund Newtonian reflector outside on a cool night and let it
cool down for a few hours. Then aim the scope at a bright star low in the sky, and look through about a 30 to 50 power lens to center the image. Set
the tracking motor to keep the star centered. Change the focus on the star from a small point to a big blob, and keep making it bigger until it fills
the field of view. I don't remember which side of the focus this is, but it's one side or the other of focus. While the star's light fills the
eyepiece you may see hazy shadows passing through the field. Have somebody put their hand in front of the telescope. You should see a very sharp
shadow of the hand if all is right, and see heated air rising off the skin. A person can position their face in front of the telescope and their
breath will be visible.
The effects are very similar to Schlieren images, in that you are using the parallel light waves from a distant star as a point source. The light
arrives essentially coherent from the star and is almost brought to a focus by the telescope. The slight differences in density allow the light to be
focused by the air density.
The effect is quite dramatic when the stars are very sharp and don't 'twinkle' too much. The twinkling is also caused by air density changes which
bend the light's path as it transverses the atmosphere.
The effect might be simulated by using a small laser reflecting off a spherical or convex first surface mirror. A chrome hubcap might work. The laser
will supply the bright coherent light, and the spherical reflection at some distance might be enough to provide the small 'point' source. I'll state
for the record you should not point a laser into the telescope, but only at a convex reflective surface in the distance.