In the last test tube add a spoonful of calcium chloride. Calcium chloride removes moisture or water. So in the first test-tube the nail is exposed to oxygen and moisture. In the second test tube the nail is exposed to oxygen moisture and salt. So when the third test tube the nail is only exposed to water. In the fourth test tube the nail is exposed only two oxygen. Stop her all four test tubes with a rubber bung and let stand for a couple of days. You will find that the nails in the first and second test tubes have rested. in particular the