This monograph is a highly technical analysis of the interaction of two phases in controlled experiments. By using a perforated plate and stirred tank, Dr Azbel has conducted experiments involving flow, mass bubbling, mass transfer during bubbling and in a liquid-solid system and the calculation of bubbling reactors for the two-phase oxidation reaction. The last chapter investigates the design of a reactor for microbiological processes. The behaviour of bubbles is a unifying theme of this book. From an explanation of the fundamentals of bubbles formation at a single orifice, Dr Azbel goes on to set up equations for bubble motion, bubble size, bubble-size distribution and pressure drop across a perforated plate. His treatment of bubbles is expanded in later chapters to include mass transfer in the dispersion of solid particles in a liquid and mass transfer accompanied by chemical reactions in a bubble dispersion system.