1.1 This part of ISO 182 specifies a method for the determination of the thermal stability at elevated temperatures of compounds and products based on vinyl chloride homopolymers and copolymers (in the following text abbreviated to PVC) which undergo dehydrochlorination (the evolution of hydrogen chloride). 1.2 The method may be used as a quality-control test during manufacture and conversion of PVC compounds, it may be used also for the characterization of PVC compounds and products, especially with regard to the effectiveness of their heat-stabilizing systems. It is suitable for coloured compounds and products where a discolouration test under the action of heat may be unsatisfactory. 1.3 The method is recommended for compounded materials and products only, although the method can be used for polymers in powder form under appropriate conditions to be agreed upon between the interested parties. It is not recommended for compounds in the form of dry blends since such materials may not be sufficiently homogeneous. PVC compounds and products may evolve decomposition products in addition to hydrogen chloride at elevated temperatures. A limited number of these decomposition products may affect the pH of an absorbing solution. It is not possible to compensate for this effect within the scope of this part of ISO 182, and therefore care is necessary in comparing results for dissimilar compounds and products. In this case, a method suitable for the determination of the chloride ions in the absorbing solution shall be used (see ISO 182-4). 1.4 The method may also be applied to other plastics materials which can evolve hydrogen chloride or other hydrogen halides when heated under the conditions prescribed by the relevant specifications, or when agreed upon between the interested parties.