Although rubber was first chlorinated in 1846 to improve its aging properties (Parks, British patent 11,147), it was not until 1888 that a product containing 65.18 per cent of chlorine was isolated and the formula C10H13Cl7 given by Gladstone and Hibbert. Nearly thirty years later the United Alkali Company marketed a solution of chlorinated rubber, Duroprene, made under the Peachey patents, and for ten years this remained the only chlorinated rubber on the market. During the past ten years interest in this material has rapidly developed, as shown by the numerous brands at present available, namely: Alloprene (I. C. I.) ; Tornesit (New York Hamburger Gummiwaaren Compagnie, later Chemische Fabrik Buckau); Tegofan (Tegofan Gesellschaft, later Chemische Fabrik Buckau); Pergut (I. G. Farbenindustrie) ; Detel (Detel Products) ; Aizen (Hadogaya Soda K. K., Japan); Nippon (Nippon Soda K. K., Japan) ; Protex (Soc. Ellettrica ed Elettrochimica del Caffaro, Italy); and Dartex (Metallgesellschaft A.-G.). The patent literature indicates that interest in chlorinated rubber is also taken by Russia, France, Austria, and Jugoslavia.