For producing paper, devices (laboratory) for determining the retention and dehydration of a fibrous material suspension, in particular under the influence of chemical additives are used. In order to simplify said tests, it is recommended to use a device comprising a measuring tank fillable with the sample of a fibrous material suspension, a filter placed on the bottom of a measuring device for covering a filtrate outflow, a protective element for covering the filter against the sample, a scissors unit for initiating shearing forces in the sample, a free keeping unit for keeping freely the filter during a retention measurement, a collector for collecting the sample filtrate, a metering unit for metering at least one chemical additive for the sample and a control unit which is constructed and connected to the protective element in such a way that the filter is covered during the retention measurement and the additive addition. |