Abstract: Two parallel cigarette rods are guided in a twin cigarette rod making machine between two stationary ionization chambers of a density measuring apparatus. Two radiation sources are mounted on a carrier between the two rods for movement with the carrier between a first position in which the radiation issuing from the sources penetrates through the adjacent rods and into the respective ionization chambers, and a second position in which the radiation enters the respective chambers by way of passages in the guides for the respective rods.

Abstract: Apparatus for making perforations in continuous or interrupted webs of cigarette paper or the like has one or more perforating units serving to direct radiant or electrical energy against selected portions of the web to make holes therein. That portion of each perforating unit which surrounds the locus of propagation of energy beyond the respective perforating unit is externally cooled and cleaned by one or more streams of compressed gas which ensure that such portion cannot accumulate solid combustion products which could interfere with the propagation of energy toward the web. The stream or streams are furnished by the orifices of nozzles which can be provided in the carrier or carriers for the perforating units or can be outwardly adjacent to the carrier or carriers.