HOw do i do the salt test (already used salt test to search)

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K this is what i plan on working with a glass penut jar with a plastic screw on cap a bottle cap distilled water and salt. How much salt and how much water should i use (and is it ok to use a penut jar cuz they would already have had salt on them.) this is my first time doing this so any info would help btw i did use the search feature and looked at the first 15 posts and didnt get this info.