This part of ISO 5263 specifies an apparatus and the procedures for the laboratory wet disintegration of mechanical pulps that exhibit latency. This apparatus and procedure are required for preparation of the test portion in a number of other International Standards dealing with pulps. ISO 5263-3 is applicable to all kind of mechanical pulps (i.e. mechanical, semi-chemical and chemimechanical pulps) exhibiting latency. Mechanical pulps not exhibiting latency shall be disintegrated according to ISO 5263-2. The procedure specified in ISO 5263-2 should 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.