6A40.30 - Index of Refraction - Wesson Oil

Code Number:
Demo Title:
Index of Refraction - Wesson Oil
Refraction and Critical Angles
Area of Study:
400 ml Beaker, Watch Glass or Test Tube, Wesson Oil, Glycerin, Immersion Oil, Karo Syrup.

A popular index of refraction demonstration is to make Pyrex glass disappear by immersion in a liquid with the same index of refraction.  Carbon Tetrachloride, Anisole, and Trichloroethylene were used extensively in the past but these are now listed hazardous carcinogens so we try to stay away from them. Immersion oil will also work but it is expensive to get the 200 to 300 ml volume necessary to immerse a test tube.

The cheaper modern day alternative is 'Wesson' vegetable oil and Pyrex glass.

NOTE: If using a test tube you need to have some of the liquid inside the tube also.

Pyrex has an index of refraction of 1.47.  The index of refraction for other common liquids are:

Clove Oil - 1. 535

Lemon Oil - 1. 481

Neroli Oil - 1.482

Orange Oil - 1.473

Safflower - 1.466

Vegetable Oil (50 degree C) - 1.47

Oil of Wintergreen - 1.536

Glycerin - 1.473

Karo Syrup has an index of refraction close to soft glass for use with stirring rods and glass cylinders.

It has been reported that Lexan and Glycerin also work well.  However, our testing indicates that Glycerin and soft glass works better than Lexan.

Mixing glycerin and water together in different concentrations will work to match most other types of glass.

The "Phantom Crystals" are commonly used as a substitute for soil in potted plants.  They are able to absorb a large amount of water and keep it from evaporating, and so they are used to keep plants from drying out under stress conditions.  The crystals are a mixture of:  25% Hydroxyethel Methacrylate, methacrylic acid, acrylimide copolymer, cross-linked homopolymer for absorption and desorption of water, and 35% silica to stabilize the system.  They have the same index of refraction as water and are therefore invisible in what looks like a beaker of pure water.  Shine a laser beam through the beaker and the beam goes straight through as you would expect if the beaker contained only water.  Pour some of the water out so the crystals are exposed and you will see the laser beam being refracted by the individual expanded crystals.

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Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.