Nanoparticles CdS, ZnS and mined crystals of ZnxCd 1-xS can be generated in situ in AOT-heptane-water and CTAB-chloroform-water microemulsions using an ultrasonic processor. The nanoparticles exhibit the "quantum size effect". The average diameter of nanoparticles, as manifested in the photoabsorbtion threshold of colloidal semiconductors, increases as the water content of reverse micelles and the concentration of ψ-state particles increases. The composition of mixed sulfides and water content (pool size) of inverted micelles can be varied systematically and the band gap energies of the semiconductor particles can be determined from photoabsorption threshold (edges). A method is proposed for determining the bulk optical dielectric constants of solid solutions of two semiconductor employing the Brus equations.