The Mixture Composition Probe (MCP) is a sensitive, in-process monitor of the composition of a fluid mixture. Sonic technology and precision electronics are combined in an insertable probe device that can monitor small changes in the composition of fluids flowing through process pipes and vessels. Real time information from the probe includes the solids-in-liquid fraction and the particle size of the solid particulates in the fluid.  In addition, the probe monitors the ratio of multiple liquid components dissolved in the mixture.