This part of ISO 5263 specifies an apparatus and the procedure for the laboratory-wet disintegration of chemical pulps. This apparatus and procedure are required for preparation of the test portion in a number of other International Standards dealing with pulps.In principle, this method is applicable to all kind of chemical pulps, including recovered fibres. It is not suitable for mechanical pulps and some very long-fibred chemical pulps such as those from cotton and similar materials.