Citation: Natta, G.; Corradini, P.; Allegra, G. (1961). The Different Crystalline Modifications of TiCl~3~, a Catalyst Component for the Polymerization of \a-Olefins. I: \a-, \b-, \g-TiCl~3~. II: \d-TiCl~3~. Journal of Polymer Science, 51, pp. 399-410.