307,945. Johnson, J. Y., (I. G. Farbenindustrie Akt.-Ges.). Sept. 10, 1927. Diolefines are obtained by heating aliphatic or cyclic paraffins or olefines obtained from mineral or artificial sources, with ¢ volume or more of steam in the presence of the catalysts specified in Specification 297,398 or of silica silicates, or noble metals. The temperature may be 600- 800‹ C. or more. Preferably the apparatus is made or lined with metals which do not cause deposition of carbon, such as chromium, vanadium, manganese or alloys such as highly alloyed steels containing considerable amounts of chromium, nickel vanadium, manganese, cobalt, molybdenum, or tungsten, a steel containing about 72 per cent of iron, 7 per cent of nickel, and 10.6 per cent of chromium being particularly suitable. In the examples, (1) 1 volume of hexamethylene vapour mixed with volume of steam is passed over lime at 680‹ C., yielding 65 per cent of butadiene and also butylene, propylene &c. (2) Equal weights of tetrahydrobenzene and steam are passed at 650‹ C. over magnesia containing up to 5 per cent of lime yielding 85 per cent of butadiene and some butylene; propylene and ethylene. The Provisional Specification states that other diluents such as carbon dioxide or nitrogen may be employed instead of steam, and is not limited as to the source of the initial hydrocarbon. Reference has been directed by the Comptroller to Specifications 27387/11 and 269,593.