Demonstrations

Density Gradient

Code Number :	2B40.50
Disclaimer:	Reprinted by permission of Dick Berg, University of Maryland, for use on this website. The demonstrations contained and referenced herein are listed for the purposes of cataloging and describing physics demonstrations which should be conducted only under the direction of a trained instructional support professional or physicist. These demonstrations are not presented for the purpose of being conducted by persons unconnected to this Facility and/or persons not consulting with or being supervised by the recognized instructional support professional or physicist and his/her staff. The University is responsible only for those demonstrations carried out using its own equipment using established safety and scheduling policies, and bears no responsibility for those choosing to use this source material for their own purposes. All demonstrations described and contained herein are public domain, and can also be found in reference materials in libraries, bookstores, and electronic sources. Further information regarding legal liability in use of demonstrations and labs will be found on the web site Injuries in School/College Laboratories in USA. The University of Iowa Disclaimers: University of Iowa Disclaimer All Rights Reserved..
Condition :	Good
Principle :	Boundary layers due to density differences
Area of Study :	Chem. and Physics
Equipment :	Salt, Water, 4000 ml beaker, Cork Pad, Funnel with hose and eyedropper nozzle, Food Coloring, Ice cubes, Hot Plate, 60 cc syringe with long blunt needle, Hero's Fountain Demo with tygon tube extensions.
Procedure :	24 hrs in advance prepare 3000 ml of saturated salt water. Carefully pour off 900 ml, color red and put in the 4000 ml beaker. The next layer is diluted to 50 percent saturated and not colored. Float the cork pad on the layer in the 4000 ml beaker and using the funnel and eyedropper gently pour the 50 percent layer over the cork so that the layers retain a definite separation. The next layer is 25 percent saturated, colored blue, and added to the beaker in the same manner. The next layer is pure distilled water, colored yellow and added in the same manner. All layers should be of about 900 ml volume. Where the blue and yellow layer mix they will produce a green layer which is why the colors I have designated work best in this order. Now, by heating with a hot plate the bottom layer will boil until it eventually mixes with the next layer which boils and mixes with the next layer etc. If the top layer is chilled and ice added the bottom three layers will be almost furiously boiling before the ice cubes are melted. If undisturbed the layers will remain distinct for several weeks. Initially when you start to pour one layer onto the other it is much easier to use the 60 cc syringe. This offers better control of the volume and speed of the added water thus giving a much more distinct boundary interface.

References

Richard M. Heavers, "Oscillations in a Linearly Stratified Salt Solution," TPT, Vol. 45, # 4, April 2007, p. 241.

Ronald M. Cosby, "Natural Convection in a Stratified Fluid", TPT, Vol. 30, # 7, Oct. 1992, p. 434.

Ronald M. Cosby, Douglas E. Petry, "Simple Buoyancy Demonstrations Using Saltwater", TPT, Vol. 27, # 7, Oct. 1989, p. 550.

David F. Paskausky, "Salinity Variation", TPT, Vol. 25, # 2, Feb. 1987, p. 73.

C. Booth, Tom Beer, and J. D. Penrose, "Diffusion of Salt in Tap Water", AJP, Vol. 46, (5), May 1978, p. 525.

Tik Liem, "Can Ice-Water Boil," Investigation to Science Inquiry, pp. 204.

"Daffy Densities", Countertop Chemistry, The Science House, North Carolina State University.

"Floating Drop of Oil," Unknown Source.

Janice VanCleave, "Mover," 200 Gooey, Slippery, Slimy, Weird, & Fun Experiments, pp. 153.

Janice VanCleave, "Sinker," Earth Science for Every Kid - 101 Easy Experiments That Really Work, pp. 196-197.

#151, "Streamers," Janice VanCleave's 204 Sticky, Gloppy, Wacky, and Wonderful Experiments.

Joey Green, "Rainbow Machine", The Mad Scientist Handbook, Vol. 2, p. 81.

Mail Questions and Comments to: Dale Stille