As the gas passes out through the valve at R the pressure decreases, permitting the water to again rise in the tube and flow through O. Gas is again generated, which at once exerts its pressure and cuts off the supply of water. This is the automatic action by which water is brought in contact with the calcium carbide. Thus it will be observed that the use or escape of the gas regulates the generation by the simple device of the rise and fall of a water column. There is a cap M screwed over the tube N. This is used to deflect the course of the water downward, so that the carbide in the lower part of the cartridge is first attacked. There is a needle inside of cap M, which can be used for cleaning the hole O. When the gas is generated it passes through the filter D on its way to the burner through R. This filter consists of a tube loosely packed with ordinary nonabsorbent cotton, which should never cover the escape pipe leading to the valve R. In passing through this cotton filter moisture and dust are removed from the gas. In the latest model a felt filter is used instead of cotton.
Fig. 6.—Signal lantern generator.
The escape pipe F provides a means for the escape of gas generated and not used or generated more rapidly than consumed. Should an excess be generated, it passes down through the tube F, and, finding its way through some small holes in the bottom of this tube, escapes through the water seal and the opening at C. It will be noted that if escaping gas at C should become accidentally lighted, the flame can not strike back into the filter and cartridge because of the water seal. The principal things to observe in the operation of this generator are the following:
(1) To see that the rubber plugs fit tightly into the openings of the cartridge.
(2) That the tube N, the cap M, and water hole O are not stopped up.
(3) That the cotton in the filter is changed frequently.
(4) That the stopcock R is closed before inserting the frame in the water. If this latter instruction is not complied with, it can be readily seen that the water will have free access to the carbide and excessive generation will occur.
When the charge is exhausted, the entire cartridge is taken out and thrown away. This eliminates the handling of carbide and the disagreeable task of cleaning out the residuum after the gas has been extracted.