To perform this test: add salt and water to a least a cup of your soil in a clear container. Use a teaspoon ish of salt per cup of earth and cover the earth with water. Shake it up. Let it sit for about half an hour. Observe and measure earth separation.

as per:

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  Fig 1: clear container + Salt

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  Fig 2: add dirt, shake, then let it sit

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  Fig 3: measure the stuff