2B40.50 - Density Gradient

See procedure.
See procedure.
Code Number:
Demo Title:
Density Gradient
Boundary layers due to density differences
Area of Study:
Chem. and Physics
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.

See also 2B40.50 in Heat and Fluids

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.

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