The method specified are applicable directly to soluted mateials or materials soluble in boiling water. In case of solid chemicals not readily soluble in boiling water, a special preliminary treatment is necessary. Precautions shall be taken in order to avoid absorption of moisture and carbon dioxide. All tests and analyses shall be carried out at a temperature of 20 °C. In order to avoid incorrect results use only reagents of analytical grade. Replaces ISO Recommendation R 1686-1970