Measuring constituent concentrations of processing liquids provides highly useful data for industrial process control. Techniques that allow online measurement will greatly save resources and energy, making them highly attractive for enterprises. In this paper, we develop a technique based on time-resolved photoacoustics for simultaneously measuring the optical absorption coefficient, acoustic speed, and thermal-acoustic transformation coefficient of an absorbing liquid, using an experimental setup that merely employs a nanosecond pulsed laser with millijoule energy and a single piezoelectric transducer with a wide frequency bandwidth. As investigated samples, we use potassium chromate, glucose, and their mixing solutions. Experimental results show that the value of each parameter measured in a mixed solution is approximately equal to the sum value of the same parameter in the constituent solutions. This means that a simultaneous measurement of these parameters enables us to calculate two or three constituent concentrations in a mixed liquid, if the constituent substances differ clearly from one another in terms of their optical absorption, acoustic speed, or thermal-acoustic transformation properties.