This International Standard describes the Soxhlet-mode parameter test to assess the chemical durability ofmaterials by measuring the initial dissolution rate in pure water. The measurement is performed at the boilingpoint of water, at which the dissolution rate is considerably higher than at room temperature. In most cases, thealteration phenomena are therefore significantly accelerated.The test described in this International Standard is intended to measure the initial dissolution rate; it is thusapplicable only to nonporous materials (or materials with small, closed porosity) for which the primary alterationphenomenon is a surface reaction mechanism (diffusion mechanisms are involved in the dissolution of porousmedia). The test results can therefore be compared only with findings obtained for nonporous materials ifserious errors of interpretation are to be avoided.The resulting “initial dissolution rate in pure boiling water at atmospheric pressure” can be used to comparematerials of the same type (e.g. oxides), provided their initial dissolution is governed by the same mechanism(e.g. surface reactions).This parameter test cannot be used to assess the long-term behaviour of a material, which generally requiresseveral tests, modelling and validation, as described, for example, in Standard ENV12920.This test is applicable to any glass, vitrified material (i.e. material resulting from a vitrification process) ornonporous oxide material with a morphology that allows the preparation of monolithic test coupons of knownsurface area. It determines the initial dissolution rate of the material in deionized water at the boiling point (approximately 100 ?C) by analysis of the leaching solution and by measurement of the specimen mass loss.