29,213. Farbenfabriken vorm. F. Bayer & Co. March 23, [Convention date]. India-rubber, preserving. - Synthetic caoutchoucs obtained from butadiene or its homologues and analogues, for example by heating #: -di-methylbutadiene with acetic anhydride, are treated with alkaline agents, for example with 2 per cent of ammonia or with a solution of dimethylamine, to prevent deterioration. The preparation of such caoutchouc is described in Specifications 15,254/10,17,734/10,25,850/10, 1124/11, 1125/11, and 6540/11, [all in Class 2(iii), Dyes &c.]. Specification 25,087/10, [Class 2 (iii), Dyes &c.], is also referred to.