The Chemical Effects of Ultrasound

D uring the early tests of the first British destroyer in 1894, Sir John I. Thornycroft and Sydney W. Barnaby noticed a severe vibration from the destroyer's propeller. They suggested that large bubbles, or cavi­ ties, formed by the spinning propeller and imploded by water pressure, were the source of the vibrations. Thorny­ croft and Barnaby redesigned the pro­ peller to reduce the vibrations from what came to be known as cavitation, but as the British navy built even fast­ er propulsion systems the phenome­ non became an increasingly signifi­ cant problem. In 1917, therefore, the navy cOmmissioned Lord Rayleigh to study the matter. He confirmed that the vibrations were due to the enor­ mous turbulence, heat and pressure of imploding cavities. Although cavi­ tation continues to be troublesome for nautical engineers, it has provided chemists with a unique environment for high-energy reactions. Chemistry, after all, is the interac­ tion of energy and matter. Specific energy sources limit the control chem­ ists have over the reactivity of matter. Ught interacts with matter on a short time scale at high energies, whereas