Polymer article and its use for controlled introduction of reagent into a fluid.
A solid polymeric body comprising a polymer matrix <sub>'</sub>containing a water-soluble reagent leachable into a fluid containing condensed water, said matrix being reagent permeative and insoluble in said fluid containing condensed water and the said body preferably having a softening point substantially above that of the temperature of the fluid .environment in which it is to be employed is useful for the introduction of an additive reagent into said fluid particularly when said fluid is located in a subterranean formation.