Ion exchangers (including base or acid exchangers) other than polymers of Chapter 39. These are insoluble compounds which, when brought into contact with a solution of an electrolyte, exchange one of their own ions for one of those contained in a substance dissolved in that solution, this property being of value industrially, e.g., for removing the calcium or magnesium salts from hard water intended for boilers, for the textile or dyeing industries, for laundries, etc. They are also used to convert salt water into drinking water, etc. Artificial zeolites (whether or not chemically defined), except those containing binders are, however, excluded (heading 28.42).