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Q & A: desalting water

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Most recent answer: 10/22/2007
Q:
is ther a machine that can change salt water into fresh water? and where would i find such a machine.
- alan lenihan
uk
A:
Alan- There are indeed many such machines. I'll just describe a few.

1. Your freezer. If you freeze salt water, the salt is excluded from the ice. If you pour of the salt water around the ice, you'll be left with almost salt-free ice. The trick here is to set the freezer not too cold, so the ice doesn't feeze too rapidly. If it freezes too rapidly, the salt can get trapped in little pockets, hard to separate from the nearly pure ice crystals themselves. It may be best to grab the ice out before most of the water has frozen.

2. A still. This is the traditional way to purify water. When water is boiled, the vapor contains almost no salt. Many other impurities are also left behind in the liquid. If the vapor then travels to a cooled coil, it will recondense into purified water.

3. Reverse osmosis. The water is forced under pressure through tiny pores. Electrostatic forces prevent most of the (charged) salt ions from enetering the pores, so the water that comes through has greatly reduced salt conentrations.

You could build your own still, or scrounge around in science supply sources to buy one. Reverse osmosis systems should be available from many commercial water purification supply companies.

Mike W.

(published on 10/22/2007)

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