Demonstration Description: A beam of white light is directed through a transparent vessel and projected on a screen. The vessel contains a mixture of water and sodium thiosulfate. Dilute sulfuric acid is added to the mixture. Colloidal sulfur begins to form and the beam passing through the liquid starts to look blue. As the number and size of the scattering particles increases, the transmitted light changes color from a bright white to yellow to orange, and then to red. Eventually even red light is no longer transmitted. It can also be shown that the light through the container becomes increasingly polarized in the process
80 cc(ml) of sodium thiosulfate crystals are mixed with 2 liters of water. Just before demo time, add 3 ml of a dilute 3% solution of (H2SO4) sulfuric acid and water. Polarimeters are used to show the light is polarized a short time after adding the sulfuric acid solution. The color of the projected image changes from bright white light to yellow, orange, then to red. At this time the lecturer changes the height of the hole to show the sun setting.
Eric Hudson pretends to cry during this demo at the end of 8.02 every year.