Date: Tue, 16 Feb 1999 10:52:27 -0600

Author: (Karl Trappe)

Subject: Re: Sunset Demonstration 6F40.10


Are you sure that wasn't sulphuric acid instead of hydrochloric? The
object is to cause sulphur molecules to precipitate out of solution over a
period of time. This gives you the setting sun, rather than the "sun set".

To limit/control the speed of this demo I keep two mixed containers of
dilute sulphuric handy. I premix my sodium thiosulfate in the water. When
the instructor is ready to perform the demo *one* beaker of sulphuric acid
solution is poured in and mixed. If the experiment needs to be hurried up,
the other beaker can be added. I use 125 gm of sodium thiosulfate crystals
in the optics display tank (the old one sold by cenco) which I fill to near
the top. My acid beakers contain about 1cc of concentrated sulphuric acid
in 125 ml of water. Warm water can also be added to speed up the process
*during the demo* if needed. Karl

>We use the Sodium thiosulfate/HCl that Vacek spoke of. I've been told that
>the Pine Sol also works. The speed of the reaction time is strongly
>temperature dependant. At room T it takes about 4-5 minutes. If the water
>is colder it is much slower, and if the water is warmer it is very fast,
>too fast. I keep the aquarium filled with water overnite so it is room T
>in the AM.
>Make a metal slide with a large hole (~1") in the center. Put it into the
>slide projector to make a sun disk through the water tank and onto a screen.
>A neat trick. With the light showing a beam path through the solution take
>a large polarizer, rotate it off the side of the tank to show that the
>reflected light is strongly polarized. Rotate it off the front of the tank
>to show that the transmitted light is not polarized. JZ
>At 03:21 PM 2/15/99 -0500, you wrote:
>>We have been using milk for the Sunset Demonstration
>>( It
>>seems like somebody somewhere said something about some kind of solution
>>that worked better. This solution scatters the blue (polarized) and allows
>>the red to pass through. As time passes, more light is scattered and
>>eventually no light gets through. Any thoughts on this.
>>Keith Warren Director of Demonstrations
>>202 Cox Hall (919) 515-2910
>>Dept. Box 8202 (919) 515-6538 fx
>>NC State University
>>Raleigh, NC 27695

Dr. Karl I. Trappe Desk Phone: (512) 471-4152
Physics Dept, Mail Stop C-1600 Demo Office: (512) 471-5411
The University of Texas at Austin Home Phone: (512) 264-1616
Austin, Texas 78712-1081