Use chemistry to make a bouncing polymer ball, then alter the procedure to see the effect the changes have on the characteristics of the bouncing ball.: Make a Bouncing Polymer Ball - Introduction and Materials
Soap qualities and how to achieve them. ~ Hardness can be increased by adding salt or sodium lactate. Sodium lactate is preferable for this purpose because salt has an adverse effect on lather, and sodium lactate helps lather, at least a little.