Does freshwater hold heat longer than saltwater?
As noted at this Ask a Scientist web site, pure water has a higher specific heat (the amount of heat needed to raise the temperature of 1 kg of a substance by 1 degree C) than salt water. Addition of salt reduces the heat storing capacity of water. This suggests that fresh water should hold heat longer than salt water, however the difference is small and other factors besides specific heat could have a greater effect. The addition of salt will increase viscosity, causing convection currents in salt water to be slower, resulting in slower heat loss at its surface and interfaces (e.g. through the sides of a container). This California students report of his experiment Comparison of Heat Retention in Salt Water and Fresh Water Samples concludes that salt water holds heat for longer. The difference seems more than I would expect. I suggest that more experiments would be a good idea.
