The Answer: Will surprise you. It can be accomplished using two different methods.
Sand or Sun ??
We are surrounded by salt water ice. Take any piece and stand it up. Scrape all the snow off the top and the sides. Let the sun do the work and go do something. IN time when you come back you will notice a difference. It is well below zero. That ice will begin to clear @ the top and work its way down. When the ice is crystal clear at the top. Take your kettle and an ice pick and chop the ice horizontal from the top down. Fill your kettle with clear chips of ice. When melted that water is delicious.
You can actually watch the 'salt' settle inside of frozen ice!!
If it is cloudy outside. Place that block of ice on sand- the sand will sux that salt down quicker! We also use sand to cut huge holes in the ice when a whale is trapped under the ice pack!!
Inupiaq technology - time tested for many thousands of years!!
Thanks for the comment
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