Metals usually corrode at a faster rate in the presence of salt. The corrosion process being studied here is assumed to be one where the copper penny is submerged in water. The effect of the amount of salt in the water on the corrosion of the coin can be determined by first assuring at all factors other than the concentration of salt in the water are the same.
This would include ensuring that the coin is totally submerged under water in all the samples, maintaining a similar temperature and ensuring the air above the water has the same concentration in all the cases. This is easily done by placing each coin in a petri dish submerged under water and placing all the dishes in a closed or open box.
One coin is maintained as a reference and placed in distilled water without any impurities or salt in this case. The percentage of salt dissolved in the water is gradually increased in the subsequent petri dishes used.
After setting up this configuration the coins should be left to undergo the corrosion reaction for the same duration of time. The coins are examined after regular durations of time to see how much they have corroded. This can be done by looking at the loss in weight of the coins, measuring the depth of pits formed due to corrosion and the alike.