Abstract: Disclosed is an improved turbidimeter or instrument for measuring the concentration of a suspension using diffuser means for converting incident light into diffused light before passing through a suspension. The use of diffused light improves the linearity of the optical density vs. concentration characteristics over a relatively wide range.

Abstract: This invention relates to an apparatus for automatically sampling a clarified test solution from a suspension to be tested, which comprises two filtering tubes being immersed in the suspension, a circulator connected to the one tube, and a sampling cell connected to the circulator and the other tube. The suspension is sucked by the circulator and filtered through the one tube. The filtered and clarified test solution is sampled in the sampling cell and the residual test solution is returned to the suspension through the other tube. A flow direction of the test solution is reversed at intervals so that the filtering tubes are not blocked by suspending solids.