Abstract: The invention provides a sampling process and apparatus therefor for the control of the addition of expensive conditioning material, referred to as polymers, to suspensions, sludges and the like, particularly sewage sludge, to facilitate its dewatering. The process employs a viscometer able to measure rapidly the shear stress of the sludge and obtain a typical peak value characteristic of optimum conditioning of the sludge. The process and apparatus also operate in a new mode involving charging a sample vessel with unconditioned sludge, taking a measurement to obtain an "unconditioned" signal, and then filling with conditioned sludge and obtaining a "conditioned" signal, the unconditioned signal indicating the solids content of the sludge and being used to modify the signal controlling the polymer flow and therefore the dosage to compensate for this charge. The viscometer rotor and the vessel interior are rinsed to remove the conditioned sludge before a fresh batch of unconditioned sludge is introduced.