Abstract: An apparatus is provided for measuring particle sizes between 5 and 50 microns in size and between 10 and 4,000 ppm in concentration prior to dilution of the sample, and upwards to at least 50,000 ppm with dilution of the sample. It is comprised of a laser light source, a square or rectangular sample cell and a photodetector which feeds data to some form of digital processor. The laser light is polarized and the return scattered light is polarized in the same plane. This device functions on the principle that particles in a light beam are capable of scattering the radiation in that beam and that the scattered radiation can be correlated to the physical properties of the scattering particles, specifically size and number.