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The effects of variations in the zinc oxide, sulfur, and mercaptobenxothiazole concentration on the sulfur combining rates were determined. It was found that a marked induction period exists, Ostcrhof and the Goodyear Tire and Rubber Co. for permission to publish this work.during which the zinc me1 captide of mercaptobenzothiazole, the initial product, reacts readily with sulfur. The ratio of combined sulfur to consumed niercaptobenzothiazole is constant during the vulcanization process. A kinetic expression is given which accounts for the data.When polyisobutylene was substituted for GR-S or Hevea, the zinc mercaptide of mercaptobenaathiazole was found to be the initial product.A mechanism is postulated for the accelerating properties of mercaptobenzothiazole. I t involves the formation of the zinc mercaptide, which reacts with sulfur and rubber t o regenerate mercaptobenzothiazole and form sulfur-rubber compounds.The author wishes to el;press his sincere appreciation to earl Parks for experimental assistance and to 8. D. Gehman for Buggestions and encouragement. He also wishes to thank H. J. SOCIETY, Buffalo, N. Y . , October 1352. Work performed as a part of the research project sponsored b y the Reconstruction Finance Corp., Office of Synthetic Rubber, in connection with the synthetic rubber program. Contribution 137, Research Laboratory, Goodyear Tire and Rubber Co.

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The bound rubber-black complex formed by milling various GR-S polymers and carbon blacks at several temperature levels was studied. The amount of bound polymer increased with greater loadings of black, but per unit of carbon black, it decreased at the higher black loadings.The temperature of mixing likewise has a large effectat lower carbon black loadings, higher temperatures increase the amount of binding; 'the effect is minimized as the loading is increased until at high loadings (100 to 125 parts of black per 100 parts of rubber) this effect is eliminated. By fractionation of the sol portion, it has been shown that polymer of progressively lower molecular weight is bound as the black loading is increased. Polymer of high molecular weight does not replace bound polymer INDUSTRIALAND ENGINEERING CHEMISTRY