What is an incompatible substance; esp., in pl., things which can not be placed or used together because of a change of chemical composition or of opposing medicinal qualities; as, the incompatibles of iron called?

incompatible — An incompatible substance; esp., in pl., things which can not be placed or used together because of a change of chemical composition or of opposing medicinal qualities; as, the incompatibles of iron. (Webster's 1913.)

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