Needed Solutions:

• Sodium thiosulfate solution (4.5 g dissolved in 700 mL of water)
• Strong acid dilution (some dilution of 0.5 mL of concentrated sulfuric acid i.e. 18.18 mL of 0.5 M sulfuric acid)

Place sodium thiosulfate solution in a transparent container in front of a high-power slide projector. Using a circular aperture at the focal point, the projector is used to image a sharp disk onto a wall or screen. Adding the sulfuric acid solution to the container causes a slow chemical reaction which results in a suspension of sulfur colloids. Other strong acids, such as hydrochloric acid may be used instead, but the amount of concentrated acid will differ based on the reaction ratios. The colloids cause the light from the projector to be Rayleigh scattered.

One may simultaneously observe blue light scattered out of the side of the container and orange light projected onto the screen. Polarizing filters are available to investigate the polarization of the scattered light and to show the effect of polarizing the incident light. As the chemical reaction progresses, the increasing number of scattering particles causes the projected disk to turn increasingly red and dark. The demonstration lasts 1-2 minutes

L1, F0, G0, sink

PIRA DCS 6F40.10