Novel photometric system

Claim 1

Apparatus for measuring the amount of light absorbed by a portion of a flowing liquid, comprising: a sample cell for transporting said flowing liquid along the longitudinal dimension of said cell, said cell including a wall extending generally longitudinally, a light entrance window at one longitudinal end of said cell, and a light exit window at the other longitudinal end of said cell; a light source for generating a light beam; masking means including a mask with an aperture positioned between said light source and said entrance window of said cell for optically shaping said beam so that the portion of said beam that enters said cell through said window is transmitted through said cell without contacting said cell wall for a predetermined maximum liquid-lensing condition, thereby assuring that wall contact does not occur under any expected condition, said maximum condition corresponding to when the liquid in said cell has a distribution of refractive index that causes the greatest expected divergent spreading of said beam by refraction, detection means positioned beyond said exit window for measuring substantially all of the light emerging from said window, said detection means including a photoelectric element onto which said emerging light beam is incident, whereby the amount of light detected by said apparatus is independent of the amount by which said beam is bent by refraction within said cell because all of said beam entering said cell and not absorbed by said liquid also emerges from said cell and is detected, thereby making said apparatus independent of variations in the refractive index of said liquid.