Protects working solutions or concentrated chemistry from oxidation. Just a quick spray into the container and the chemistry will stay fresh twice as long. The gas is heavier than air and so it sits on the surface of the chemistry like a lid. You don't need to fill the whole chemisty canister with gas - just a quick spray does the trick. This should never go missing from any dark room! 1 can should last a lifetime (unless you use way too much of it...)
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