The construction and the principle of operation are exceedingly simple, as may be gathered from reference to Fig. 16. The beacon comprises a gas generator tube of steel (1), which is supported by the steel float chamber (2), on the upper side of which is placed the support (3) carrying the lantern (4). Stability is insured by means of the counterweight (6) attached to the lower end of the generator tube. A few feet from the bottom of the latter is a diaphragm (7), fitted centrally with a conically-seated valve (8) which is mounted on a stem (9). This extends through the centre of the generator and its head (10). The upper end of the valve stem carries a hexagonal nut (11), while the stem itself at this point has a keyway cut into it. A spline is fitted into the generator head to engage the keyway, and when the nut (11) is turned to close or to open the valve, the stem itself cannot move with it, except in two directions only--up or down. The nut itself cannot be turned too far, in which event it might drop the stem and valve, as there is a stop-collar (12). Leakage of gas is prevented by a cap (14), which is screwed into the generator head and sealed with a rubber washer. This cap is sufficiently long to permit the valve stem to be raised or lowered so as to adjust the movement of the valve. The stem of the valve is protected from the carbide by enclosure within a tube (13), which works through a guide bar (24) bolted to the side of the generator tube. A grid (23) is fitted in the centre of the diaphragm (7) and surrounding the valve (8), so as to prevent small pieces of carbide, which may pass through the grate (16), from falling into the water, and thereby being wasted. The steel grate upon which the carbide rests is attached to the inside of the generator, a short distance above the diaphragm. The grid (23) also acts as a valve seat, and is provided with a rubber packing (15), which is held in a groove in the seat, and projects a sufficient distance to make a good joint with the valve (8) when it is closed, even if the valve happen to be foul. The carbide of calcium, in the form of large crystals measuring about 8 by 4 inches, is placed in the generator tube when the beacon is immersed in the water, the valve (8) being opened and the valve-cap (14) screwed down. In the centre of the counterweight (6) is an orifice through which the water enters from the outside, and passes through the open valve, to come into contact with the carbide resting upon the grate. Gas is generated instantly, to ascend through the carbide into the purifying chamber (5), where all deleterious matter is removed, the gas escaping thence through the small aperture (17) and pipe (18) to the lantern, to which the supply-pipe is connected by the aid of the coupling (19).