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6A40.31 - Disappearing Crystals

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​6A40.31 - Disappearing Crystals

Title6A40.31 - Disappearing Crystals

Demonstrate how an object cannot be seen when immersed in a substance with the same index of refraction.

Assembly Instructions


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.

Setup Time10
Operation Time
Preview Time5
Operation Instructions
Demo on DimeNo
PIRA 200Yes
Export Instructions (if different)
Category6 Optics
Subcategory6A - Geometrical Optics
Keywordsreflection, refraction, index of refraction
Construction Information
beaker 500 mL glass
water - de-ionized
hydroxyethel methacrylate, methacrylic acid, acrylimide copolymer, silica crystals (baby diaper filling)
Old Setup: two beakers, glass prism, tongs, glycerin or benzene + CCl4 solution