+ X 0 + A I , is given by an expression of the type ES and if the equilibrium constant is given by an expression of the form (which is approximately true), then the recombination constant will be given bywith a similar expression for kg. The factor *1 is about the same for the two reactions. From a simple viewpoint the PZ factors would also be about equal. \$'ith s = 3 the ratio of the (En/ Rl')s-l terms contributes a factor of about 9 to ks k2. The rest of the difference in the rates of the 0 + NO + M and 0 + Os + 11 reactions remains unexplained.Acknowledgments.-The support of this work by the Office of Naval Research is gratefully acknowledged. Lye thank Professor S. W. Benson arid Dr. 0. K. \ITulf for helpful discussions and Professor R. 11. Badger for the loan of the spectrograph. Lye are much indebted to Dr. R. E. Duff for making his computing codes available to us LT. 11. Jones expresses his appreciation to the In an effort to elucidate the mechanism by which phenols retard vinyl polymerization in the presence of air, the action of twenty phenols upon the polymerization of methyl methacrylate has been studied Induction periods and rates of polymerization have been measured dilatornetrically. .kddition of a phenol increases the length of the inhibition period iuvcr that due to oxygen alone. A % kinetic scheme has becn developed which accords well with the cxperirnental results. On this basis it is concluded that phenols act as anti-oxidants, as is often found to be the case in other free-radical reactions. The phenol prevents oxygen from becoming depleted too rapidly, thus extending the inhibition period by niaintaining a reasonably high os>-gen concentration level for a longer time than would normally be the case. Relative eficiencies of several phenols have been determined and these results correlated with other kinetic studies of oxidation inhibition by phenols.

The oxidation of benzoin to benzil in alkaline alcoholic solution gives rise to a purple colored intermediate. This has previously been interpreted a s a bimolecular compound akin t o a quinhydrone and later as a semiquinone free radical. The magnetic susceptibility of the oxidizing benzoin system has been investigated and the intermediate identified as a relatively stable free radical, an aliphatic analog of the semiquinones. In the course of this work a "slow oxidation" technique has been developed. Purely chemical tests indicate the presence of more labile radicals, either hydroxyl or perhydroxyl or both. The available evidence indicates that a non-chain free radical mechanism is operative in the benzoin oxidation.

Describes the Wilhelmy method and an apparatus and procedure for measuring contact angle.

No abstract

No abstract