Does salt water hold up less weight than pure water? Surface tension (the thin film on the water's surface) is what keeps a small piece of foil floating. You fill two beakers with distilled water and add salt to one. You cool both to 15°C and float a 1 cm square of aluminum foil on each. Then you drop rice grains onto the foil one at a time until it sinks. You repeat this at 25°C, 35°C, 45°C, and 55°C. Comparing grain counts across all temperatures reveals how salt and heat each reduce surface tension.