7701. Le Rond, L. J. J.-B. April 7. [Patent of Addition to No. 4129, A.D. 1908.] Furnace - gas engines. - Relates to improvements in the motor described in Specification No. 4129, A.D. 1908, and comprising an aircompressor which works without clearance, a heater-vaporizer adapted to produce a hot motive fluid consisting of a mixture of compressed air, combustion products and steam, and an engine working upon the "recuperating cycle" principle as described in Specification No. 1849, A.D. 1908. The improvements relating to the single-acting compressor described in Specification No. 4129, A.D. 1908, are in the present case applied to double-acting compressors. Fig. 1 shows an arrangement of valves for a double-acting compressor adapted to work without clearance. Two suction valves, which are arranged in the piston, are rigidly connected to the hollow piston-rod p which forms the air inlet passage. The piston provides a guide P' for the piston-rod, and oppositely-disposed seats for the valves, which thus operate alternately while serving as the driving- link between piston-rod and piston. The delivery valves wholly cover the cylinder ends and permit the stroke of the piston to exceed the length of the cylinder. In a modification, a suction valve is arranged centrally in each delivery valve. Fig. 3 shows a valved piston made in two parts having cylindrical or conical jointing-surfaces C. The pin which secures the piston to the connecting-rod is held in place by screw-threaded engagement with the valve-guiding portion F of the piston. In the heater-vaporizer, Fig. 6, a burner B for liquid or gaseous fuel is arranged at the entrance to a combustion chamber C located within a boiler D. Compressed air admitted through the pipe G circulates through annular flues H, I, a portion then passing directly through passages K to the combustion chamber while the remainder passes into the burner so as to mix with the fuel before ignition. Water entering the boiler through the pipe E descends as steam through vertical pipes m and mixes with the combustion products at the exits of the fire tubes l. The steam issues through oblique holes in a ring n, producing a helical movement which ensures thorough mixing. In another form of heater-vaporizer, Fig. 7, the water is converted into steam and mixed with the combustion products by direct contact with them in a flue A provided with various forms of baffles in order to make the contact as intimate as possible. The water is caused to fall in cascades over ledges formed by horizontal or dished annular rings, Figs. 8, 9, and 10, preferably provided with radial ribs, Fig. 12, or it is caused to traverse a helical channel between helical rings of similar construction to the ledges. The rings may be perforated, made from wire netting, or they may be separated by wire netting. An annular ring with ribs may be made from a rectangular sheet by a folding process. Drip water falls into a tray and is quickly evaporated. The combustion products may, if desired, be forced upwards through the descending water; Fig. 4 shows a valve for the engine which is similar to the valve shown in Fig. 10 of Specification No. 4129, A.D. 1908, except that the conical portion A is in the reverse direction. Variable distribution is effected in the engine cylinder by means of valves actuated by two or more cams of the same profile arranged on concentric spindles and adapted to present a variable projection ranging from that due to a single cam to that due to the cumulative effect of all the cams. Fig. 5<a> shows two cams having similar profiles A to E, G to K, mounted on concentric spindles a<1>, b<1>. The cam on the spindle a<1> may be independently rotated between limits defined by stops L<1>, L<2> so as wholly or partly to coincide with the other cam. The compressor may be operated directly from the engine, that is to say without connecting the respective piston-rods through the medium of a crank-shaft. Thus in Fig. 13 the piston-rod 3 of the compressor is shown as being directly connected to an arm 2 of the piston-rod of the engine. In a modification, the piston-rods are connected by a beam pivoted centrally to a suspension link. In a further modification, the suspension link is replaced by superimposed horizontal guides in which the pivot of the beam slides. In order to separate the condensed water from the steam, or to condense the steam, the exhaust from the engine may be passed through an aircooled condenser comprising a number of thin metallic helical tubes connecting an upper inlet box with a lower box, provided with wire netting or baffles, in which the condensed water is separated and retained. Centrifugal separators may be employed, or the steam and water may be allowed to bubble through a liquid, which retains the water. Non-return valves and relief valves are provided between the heater-vaporizer and the engine ; the relief valves may communicate with alarm devices. Starting may be effected by means of a crank or pedals which, when the apparatus is employed on a motor vehicle, may be operated from the driver's seat. Alternatively, starting may be effected by compressed air from a storage tank supplied by the compressor or by an independent pump, e.g. a pump for inflating the tyres.