Number 58 (Story #4), December 5, 1991 by Phillip F. Schewe and Ben Stein SONOCHEMISTRY AND AMORPHOUS IRON are two of the things possible with sonoluminescence, a phenomenon in which ultrasonic sound waves passing through a liquid cause bubbles to rapidly form and then collapse, emitting visible light. This "cavitation" process whereby sound energy is converted into concentrated light energy is still poorly understood, yet it is being put to practical use. The high temperatures (5000 K) and high pressures (500 atm.) arising from cavitation can be used to accelerate chemical reactions. Furthermore, Kenneth Suslick of the University of Illinois has used cavitation to create an amorphous iron powder; the bubbles first liberate the iron atoms from a molecular solution and then quickly freeze the iron before it can form into a crystal. The cooling rate was estimated to be more than the 105 to 107 K/sec rates normally needed in making other metallic glasses. Amorphous iron may have commercial applications in the sound-recording industry. (Physics Today, November 1991.)