1) Take three test tubes and place clean iron nails in each of them.
2) Label these test tubes A, B and C. Pour some water in test tube A and cork it.
3) Pour boiled distilled water in test tube B add about 1 ml of oil and cork it. The oil will float on water and prevent the air from dissolving in the water.
4) Put some anhydrous calcium chloride in test tube C and cork it. Anhydrous calcium chloride will absorb the moisture if any from the air. Leave these test tubes for a few days and then observe.
Observation : Iron nails rust in test tube A but they do not rust in test tubes B and C. In the test tube A, the nails are exposed to both air and water. In the test tube B the nails are exposed to only water and the nails in test tube C are ex¬posed to dry air.
Inference : From this we can conclude that both air and water are necessary for corrosion of iron.