M7-31 TYNDALL'S EXPERIMENT - COLLOIDAL SUNSET

M7-31

Colloidal sunset demonstration

The collimated white light from the bright point source passes through the empty tank and hits a nearby screen. Chemicals previously prepared are then mixed in the tank: 2.5 ml sodium thiosulfate solution in 100 ml water, and 2.5 ml concentrated HCl 1:4 dilution in 650 ml water. When the chemicals mix they begin to form a suspension of sulfur particles which act as scattering centers for the light, especially blue light at first. This leaves the light on the screen with a yellowish tint. As time passes the sulfur particles grow larger and scatter more light and light of a longer wavelength, changing the light on the screen to a bright red. Ultimately most light is scattered, leaving no light on the screen.

M7, LS1, OM1