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When the marker has been prepared for use and dropped into water, the water jacket fills and the scalloped disc in the main valve and the large disc in the pilot valve are forced against the ledges in the valves, thus preventing too great an ingress of water while it is submerged. Some water, however, enters the main outlet tube, passes through the pressure plate, and reacts with the calcium phosphide. This reaction evolves impure phosphine gas, which ignites spontaneously when the marker surfaces. As it surfaces, the pressure against the valves is relaxed, and the springs return the discs against the circlips, thus permitting the ingress of water through the scallops in the disc to the bottom of the inlet tube and pilot tube. The water entering the main valve passes through the inlet tube into the perforated tube, and after passing through the perforated diaphragm percolates through the flannel sheath and reacts with the main charge to give off pure phosphine, which is not spon¬taneously inflammable. The cap over the free end of the perforated tube prevents the water from percolating through the part of the flannel she a,! h above the pressure plate,
The water entering the pilot valve percolates through the flannel disc and dissolves the po¬tass ium bisulphate and the sodium nitrite. The chemicals interact and evolve gaseous oxides of nitrogen which mil with the phosphme in the strainer. The mixed gases are spontaneously inflammable in air, and, passing through the main outlet tube, ignite immediately on reaching: the air. The flame thus produced continues to burn evenly for approximately two hours, during the whole of which time the gases remain spontaneously inflammable, so that even if the flame is put out by a wave, it lights up again as soon as contact with air is re-established.
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