TAPPING-OUT AND STOPPING-UP FURNACES, ETC. 93
it is simply a 2-inch g-as pipe leading from the hot blast pipe (cold blast can also be used), into which a j^-inch pipe D carries a stream of coal oil. This is contained in a can sufficiently high to force the oil out and overcome the blast pressure at the outlet; there it ignites by combination of the air and oil. Sufficient heat is thus generated to melt the iron or enable it to be knocked away. Space is made, in this manner, which admits the blast and metal blowing out to further cut away the solid iron to a point warranting the replacing of the notch for regular working. In some cases a coke or coal fire may be encased in front of the blow pipe, and the stock is to be cut away as illustrated by the small lumps of fuel seen at E, Fig. 19. The principle involved in this process is one which may often be practically applied by the founder in preparing a casting to be burned, by bringing the point ot fracture to almost a molten state, thereby saving labor of melting and handling a large quantity of molten metal. It may at times also be found of value in assisting to cut away heavy bodies of iron that may be found almost impossible to be otherwise manipulated. In using this device to cut out a notch of a furnace, great care is exercised, as it may cut through the chilled material and, without warning, the molten contents may burst out with such force as so serious that furnaces have had to " blow-out" to remove them. A method sometimes employed to gain access through solidified iron, which had closed up tuyeres, or a " notch," so as to prevent its being tapped, is that illustrated by the hydrogen blow-pipe at A, Fig. 19, page 93. As used in this case,ch oftener than when it can be tapped at the regular notch. It is often surprising how rapidly, as about 75 per cent of the heat generated from the solid fuel is utilized. This is attained where one ton of coke will produce one ton of iron; and Sir........................ 2,720 "