Abstract: Method and apparatus for determining the concentration of dissolved solids in a sample solution. A refractometer has an enclosing opaque housing, a light source directing a substantially collimated monochromatic light beam through, and a hollow transparent-walled prismatic container adopted for holding a liquid solution to be tested. A light sensor is disposed in the refracted path of the light beam and responds to the exact refraction of the beam caused by passing through the liquid solution. A display is actuated by the light sensor and digitally displays the exact refraction as a function of the concentration of dissolved solids in the liquid sample. Method and apparatus are provided for determining the presence of a sufficient amount of the sample and for automatically commencing the testing in the refractometer.