6A40.31 - Disappearing Crystals
Demonstrate how an object cannot be seen when immersed in a substance with the same index of refraction.
Drop approx. 10 hydrated crystals into a beaker full of deionized water. Wait approx. 15 min for the crystals to expand. Once expanded, they have the same index of refraction as water. Pour out water to show how much crystals swelled. You can also take a beaker full of already swollen crystals and pour water into the beaker to watch the crystals disappear.Old Procedure: A glass prism is partially immersed in a beaker of glycerine or better, benzene + CCl4 solution. Keep the benzene + CCl4 covered with the watch glass when not in use. The indices of refraction are nearly identical so the portion of the prism immersed is almost invisible. Next, immerse the prism in a beaker of water to show that the prism does not disappear in water.
Note for Dehydrated Crystals
Please, use DEIONIZED WATER, and DO NOT TOUCH with your hands. Using tap water or touching the crystals will contaminate them, and the crystals will only be good for one use.