CONCENTRATION MEASURING INSTRUMENT

PURPOSE:To widen an application range by providing a porous tubular body through which a material to be measured in sample liquid passes and a light emitting element which is arranged through a fiber for light emission, and detecting outgoing light and measuring the concentration. CONSTITUTION:The material S to be measured in the sample liquid B introduced in an external frame body passes through the porous body constituting the tubular body 1 and reaches the internal wall surface side of the tubular body 1 and is dissolved and diffused in the medium A in the tubular body 1. In this case, the material S which is dissolved in the medium A toward the tubular body 1 has a difference in concentration and consequently a refractive index distribution is generated in the same direction. Light which is made incident on the medium A from one end of the tubular body 1 is received by a light- receiving part on the other end part to observe variation in the beam diameter, energy density, or convergence point of the projection light. Namely, the extent of this variation is varied with the concentration of the material to be measured. The variation quantity and the concentration of the body are in constant relation, so this variation quantity is detected to measure the concentration.