3500.     TURKEVICH, J., AND SELWOOD, P. W.  Solid-Free Radical as Catalyst for Ortho-Para Hydrogen Conversion.  Jour. Am. Chem. Soc., vol. 63, 1941, pp. 1077-1079; Chem. Abs., vol. 35, 1941, p. 3512.

        Object of this investigation was to determine whether the list of solid substances catalytically active for this transformation could be extended to include solid free radicals.  The organic free-radical chosen for the investigation was a, a-diphenyl-β-picrylhydrazyl (I).  The magnetic characteristics of (I), the corresponding hydrazine, active ZnO and ignited ZnO were determined.  H₂ adsorption at liquid-air temperature was determined on (I), active ZnO, and an intimate mixture of the 2.  Ortho-para H₂ conversion at liquid-air temperature was slow on ZnO and slow on the free radical but very rapid on an intimate mixture of the 2.