This part of ISO 5263 specifies an apparatus and the procedures for the laboratory-wet disintegration of mechanical pulps that do not exhibit latency or mechanical pulps where latency has already been removed. 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 mechanical pulps (i.e. mechanical, semi-chemical and chemi-mechanical pulps) that do not exhibit latency, including recovered fibres from mechanical pulps. It is not suitable for mechanical pulps exhibiting latency for which the disintegration procedure described in ISO 5263-3 shall be used. The procedure specified by ISO 5263-2 should also be used to disintegrate all mechanical pulps to be measured for brightness. NOTE Brightness is not significantly altered by the presence of latency; however, hot disintegration of mechanical pulps can lead to significant loss of brightness.