Tyndall Effect

The Tyndall Effect is caused by reflection of light by very small particles in suspension in a trasnparent medium. It is often seen from the dust in the air when sunlight comes in through a window, or comes down through holes in clouds. It is seen when headlight beams are visible on foggy nights, and in most X-File episodes when Moulder and Sculley check out some dark place with flashlights.

Tyndall effect is easily seen using a laser pointer aimed at the the mist from this ultrasonic humidifier's mist

In liquids the tyndall effect can be easily seen by using a laser pointer. If you dilute milk to where it is almost clear, or if you have any type of sol, such as colloidal silver, then the beam of the laser can be easily seen as it travels through the liquid.

Tyndall effect is seen here using a laser pointer. The glass on the left contains 5 ppm of HVAC colloidal silver and the one on the right is from the tap after the bubbles have settled out. Fairly large particle size was used for this demonstation so it could be caught by the camera in broad daylight. True high quality CS will have a faint, but perceivabe tyndall when viewed in a darkened room.

For any particular particle size, tyndall will increase linearly with concentration (ppm). However since tyndall will increase to the third power of particle size for any given concentration, it is very difficult to use tyndall to determine concentration of a sol. Tyndall can really only be used as a go/no go test to determine if a colloid is present, not its concentration. For instance, if you have a 1 ppm sol of 10 nm particles, the tyndall will be 100 times brighter than a 10 ppm sol of 1 nm particles, instead of 1/10 as bright. This is a good test to run since the highest quality CS will be crytal clear, and thus hard to distinguish from pure water.

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