Directions for Making the Cup.
To make this cup take a piece of 4-inch lead pipe 7 inches long (an ordinary piece of 4-inch lead soil pipe will do); flange out one end and burn in a flat bottom. Three inches from the bottom, and in the side of this 4-inch pipe, burn in a trap screw, a, Fig. 19, a screw taken from an old lead trap being just the thing. This is to regulate the hight of the solution in the cup. Now make a top by taking a piece of lead and raising it about ¾ inch; punch two holes in this top, b and c, large enough to let a ⅜-inch lead pipe pass through; flange out the top of the cup and fit and burn this top in place. Take two pieces of ⅜-inch lead pipe, one to be 3 inches long and the other to be 10 inches long, and with the dresser draw one end of each to nearly a point, so that the hose can be slipped on tight. The long piece c should now be slipped through one of the holes in the top of the cup, holding it ½ inch from the bottom d and burning it in. This is the gas inlet and should be marked as such. The short piece is then placed in the remaining hole and burnt in place. The action will be thus: The gas entering the gas inlet pipe is caused to pass through a solution of blue vitriol 2½ inches deep, when the acid is caught and the gas is scrubbed and rendered as nearly pure as possible. It then enters the outlet pipe and is ready for use. If the directions have been followed the cup will resemble the illustration Fig. 17. No trouble will be experienced with this cup.
Fig. 19.—Fire Trap and Scrubbing Cup.
CHAPTER VIII.
THE FLAME AND ITS MANAGEMENT.
Before attempting to light the gas the operator must be sure that all the air is exhausted from the tubes. Otherwise the flame will go back and explode in the tubes or fire trap. To be sure of this the beginner must test the gas. A handy test tube can be made by capping one end of a piece of ½-inch pipe, which should be about 6 inches long. To test the gas, first open wide the gas cock M on the generator, Fig. 1. Then open the gas cock f on the mixing fork and let the gas displace the air in the tubes, which it will do in about one minute. Then invert the test tube, Fig. 20, and hold it over the blow pipe tip for a moment until the gas has displaced the air in the tube. Then quickly place your thumb over the opening of the test tube, which will keep the gas from escaping. Close the gas cock f on the mixing fork, then take the test tube to one side away from the generator, still keeping it inverted, and bring it close to a lighted match or candle. It will light with a pop, and if it is free from air it will burn quietly down in the tube until the gas is exhausted. Continue to test the gas in this manner until it burns as described, when it may be safely lit at the jet without fear of its burning back. This precaution is necessary only after opening the generator for some purpose.
Fig. 20.—Method of Testing Gas.