. The art of lead burning; a practical treatise explaining the apparatus and processes. ubes or fire trap. To be sureof this the beginner must test the gas. A handytest tube can be made by capping one end of apiece of ^-inch pipe, which should be about 6inches long. To test the gas, first open wide thegas cock M on the generator, Fig. i. Thenopen the gas cock / on the mixing fork and letthe gas displace the air in the tubes, which it willdo in about one minute. Then invert the testtube. Fig. 20, and hold it over the blow pipe tipfor a moment until the gas has displaced the airin the tube. Then
. The art of lead burning; a practical treatise explaining the apparatus and processes. ubes or fire trap. To be sureof this the beginner must test the gas. A handytest tube can be made by capping one end of apiece of ^-inch pipe, which should be about 6inches long. To test the gas, first open wide thegas cock M on the generator, Fig. i. Thenopen the gas cock / on the mixing fork and letthe gas displace the air in the tubes, which it willdo in about one minute. Then invert the testtube. Fig. 20, and hold it over the blow pipe tipfor a moment until the gas has displaced the airin the tube. Then quickly place your thumb overthe opening of the test tube, which will keep thegas from escaping. Close the gas cock / on themixing fork, then take the test tube to one sideaway from the generator, still keeping it in-verted, and bring it close to a lighted match orcandle. It will light with a pop, and if it is free 74 THE ART OF LEAD BURNING. from air it will burn quietly down in the tubeuntil the gas is exhausted. Continue to test thegas in this manner until it burns as described,. Fig. 20.—Method of Testing Gas. when it may be safely lit at the jet without fearof its burning back. This precaution is neces-sary only after opening the generator for somepurpose. Regulating Volume and Pressure. This generator evolves gas under a greaterpressure than can be used on most work, and forthis reason the flame will at first be long, noisyand unsteady, as shown in A^ Fig. 21, but, asthere are two cocks, the volume and pressure canbe regulated to the requirements of the work at THE ART OF LEAD BURNING. 75 hand. Now, to note the pecuHarities of thisflame, we will close the gas cock / on the mixingfork until the flame is about 3 inches long. Itwill be of a pale reddish color and will burn stead-ily. The inner flame is not as yet very well de-
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