Optical absorbance meter

DETAILED DESCRIPTION It is an object of the present invention to provide an optical absorbance meter having a simple structure and preventing irregular reflection of light on the inner wall of the flow passage.
In accordance with the present invention, there is provided an optical absorbance meter comprising a flow passage for liquid to be tested, each end of which is closed with a convex lens or a flat light-transmission plate, an introducing path for introducing liquid to the flow passage and a discharging path for discharging the liquid from the flow passage wherein light from a light source is incident from one side near the convex lens or the flat light-transmission plate and emits from the other side near the convex lens or the flat light-transmission plate, the optical absorbance meter being characterized in that: a first optical aperture is disposed in front of the convex lens or the flat light-transmission plate at an incident side; a second optical aperture is disposed in rear of the convex lens or the flat light-transmission plate at an emission side; the aperture diameter of the first optical aperture in the direction perpendicular to the axial line of the flow passage is equal to or smaller than the smallest diameter of the flow passage in the direction perpendicular to the axial line of the flow passage, and the aperture diameter of the second optical aperture in the direction perpendicular to the axial line of the flow passage is equal to or larger than that of the first optical aperture.