Powered by saltwater, this easy-to-build fuel-cell car provides a low-cost introduction to clean-energy technology. Experiment with salt-to-water ratios for various effects on performance. Activate the magnesium sheet (3 included) in the fuel-cell module to run the car continuously for 5 to 7 hr. To park, remove module, rinse with tapwater, and dry. Size, 6 x 8-1/4 x 1-3/4". Instructions included. Some assembly required.