Date: Mon, 08 Nov 1999 17:31:31 -0600

Author: Gary Karshner

Subject: Re: Sunset demo


I use 20 ml of saturate sodium thiosulfate solution per liter of water in
the tank. To start the reaction I add about 12 ml of hydrochloric acid per
liter of water in the tank. These concentrations make the experiment run
fairly slowly so the instructor has time to talk about what is happening.
Make sure that there is no acid in the tank before adding the thiosulfate.
With the more advanced students I handout polaroids to show that the light
coming out the sides is polarized. Too concentrated a solution or two much
acid makes the reaction go faster and to weak a concentration means the sun
will not set. I have only had one failure with is setup, when I didn't
watch the concentrations of solutions.
I hope this helps.


Gary Karshner

St. Mary's University
San Antonio, Texas