Abstract: A detector used in apparatus for measuring variations in the composition of a liquid includes a cell utilizing the Christiansen effect on light transmitted by the liquid flowing through the cell filled with particulate matter. The liquid and the particulate matter have indices of refraction that are substantially equal to one another at a specific wavelength. Variations of the transmitted light can determine changes of the refractive index of the liquid.Differences in the intensity of light transmitted through a sample cell and a reference device can be determined.