CYLINDERS, GAS Annealed steel cylinders, tested hydraulically to withstand a pressure of 3,000 lb. per square inch, and charged with compressed gas—oxygen, hydrogen (generally, coal-gas), dissolved acety lene, etc. Periodical re-annealing is necessary, and the gas compressing companies will not take the risk of filling cylinders unless their regula tions in this connection are complied with. The construction of the valve is such that all dust and grit should be prevented from entering it ; and therefore before connecting the fittings the valve should be opened for an instant so that the rush of gas may dislodge anything in the way. Cylinders of compressed gas are used by the lanternist, who must become familiar with the working of the valve, a cross section of which is shown in the illustration. The valve is screwed into the cylinder, the gas from which leaves by the narrow passage A when the spindle B is slightly withdrawn by turning its squared portion C by means of a key ; the gas passes to the lantern fittings through the inverted cone D. The gas-tight joint with the automatic regulator or reducing valve (one of these is necessary to reduce the pressure of the gas and provide a convenient means of attaching the rubber tubing), is made entirely by mechanical means, and all daubing of the screw threads with soap, grease, red-lead, etc., must be strictly
avoided ; accidents have been caused in this way. The stem B of the regulator or reducing valve is itself threaded, and has an adapter r upon it. Screw this adapter close to the shoulder G of the fitting ; without any rela tive movement between stem and adapter, screw the latter into the cylinder valve ; in this way the cone on the end of the stem will go home into the inverted cone D of the valve. When it can go no further, it may be found necessary to undo the fitting by, say, the third of a turn, and then screw the adapter in as far as it will go. Cylinders and fittings for oxygen are frequently painted black, and for hydrogen red; on the former the screw threads are right handed, and on the latter (See also " Limelight.")