Abstract: A coil body with an upper section and at least one lower section which has a downward cone shape. The coil body is manufactured from a thermosetting plastic by an injection molding process such that the lower section is provided along its full length with a thin molded tab. Furthermore, an injection mold for forming of the coil body is provided. The lower section of the mold is equipped with at least one blind cavity which is connected to the mold cavity via a gap running the entire height of the mold cavity.

Abstract: To effect a quasi-isothermal catalytic reaction of SO.sub.2 to SO.sub.3, a plurality of consecutive rows of banks of cooling tubes, are provided in the bed of shaped catalyst bodies in a contact reactor in such a manner that the banks of succeeding rows are staggered from the banks of the preceding rows. The distance between the cooling tubes in the banks is so selected that a penetration of entire catalyst bodies into the banks will virtually be prevented. The banks are so designed that the pressure drop of the gas in the banks is approximately the same as the pressure drop in the layer of catalyst between the bank. The distance between the banks is larger than the width of the banks.