Air, Table Salt and Water in a Home Experiment about Mars

This "proof of concept" home lab experiment very simply verifies that ordinary table salt can absorb moisture from a humid atmosphere.

The minimum equipment required is a waterproof and airtight container to hold a smaller container or bowl. Add a little water to the larger container; place the smaller bowl inside the container, and add dry table salt to the bowl. Seal the container; wait a few days; and check for moist table salt.

The image shows a second large container with the same amount of water but no bowl; this is the control. For a proper comparison, it should also have held a small bowl that had no salt. If the empty bowl ends up with a puddle of water, then either "rain" or "dew" must have occurred.

The second initial image shows the small amount of dry salt that was added to the bowl. This is a 1/3 cup measure, which was also the amount of water added to each container.

The third image shows the bowl with dry table salt, seated in the sealed container containing 1/3 cup of water.

After about 48 hours, it was clear that the salt had absorbed some water. However, this experiment wrapped up after some 72 hours.

It was difficult to see any difference in the amount of water retrieved from each waterproof container. The goal, of course, was to find less water in the "control" container. Since some water clung to the outside of the bowl, the control apparatus should have started with a bowl also.

The bowl held some visible liquid, and the salt was quite wet. Clearly water had been attracted to the salt.

Both Earth and Mars would have salty soil, rather than pure salt. Test conditions could include pure table salt (NaCl); various mixtures of sand or loam with salt; and various mixtures of calcium chloride (CaCl) with soil or sand.

The control apparatus should start with an empty bowl of the same size as the other bowls.

The experiment might have results within 24 hours if the small bowl were to sit in a broader container. This would provide a larger water surface, permitting quicker evaporation.

Weight should be included as a metric for this experiment. The key weight at the start is the "dry" bowl plus salt and sand or soil. At the end, dry the outside of the bowl and then weigh it with its contents. Any additional weight should represent the additional water absorbed from the humid atmosphere. A postage meter might be sensitive enough for this purpose.

A different proof of concept uses an uncovered bowl with the salty absorption medium. The speed of the reaction would depend on atmospheric humidity. In my home, heated for winter, the uncovered wet salt was much drier within a few hours.

Finally, this process could be tested in a refrigerator or outdoors during the winter. Will the brine stay liquid below the freezing temperature of pure water? Will the bowl continue to draw moisture from the atmosphere in conditions below room temperature?

Some people add a few grains of raw, dry rice to a salt shaker (or "salt cellar"), intending that the rice will keep the salt from absorbing water from the atmosphere. Consider testing this with the apparatus in this experiment. Did the weight increase without the salt mixture becoming wet and sticky?

Or just put grains of rice into a bowl (inside the humid container), without any salt. Again, the question is whether the rice gets heavier after a few days.

Salt is used as a preservative, because bacteria that spoil meat have trouble surviving or reproducing in highly salty conditions. If the wet salt mixture is left uncovered, and retains its moisture, examine the brine under a microscope after a few weeks. Are any microbes still visibly alive?

Scientists continue to seek for life in extreme conditions. This experiment demonstrates that salt can draw water from the atmosphere, setting a stage with the potential for supporting life.

Reference:
"Antarctic salty soil sucks water out of atmosphere: Could it happen on Mars?". PhysOrg. (Feb. 27, 2012). Accessed March 3, 2012.

Please Add Your Comments!

Did you try this experiment? Did it work?

Did you do the simple "proof of concept", or did you carefully log the "before" and "after" weights of your test mixtures?