CAUSE AND EVILS OF SCAFFOLDING, ETC. 57 dla. Charging any one to form some conception of the damage that could be done, and the reason all hands around a furnace have good cause to fear a slip. The scaffolding of a furnace can prove so disastrous as to disable or make unsafe its working parts. The author has seen a slip cause such an explosion as to lift the bell and hopper F. and K, Fig. 13, throwing them out almost on top of the furnace platform, and straining it to such an extent that it was a question whether it was safe to ^rely on the furnace shell; and he has heard of a bell and hopper being thrown about twenty feet from a furnace. Plans have been adopted to relieve sudden gas pressure, some of which are working very satisfactorily, especially the system used at the Alice Furnace, Sharpsville, Pa., designed and patented by Mr. P. C. Reed, the furnace superintendent, and shown in Fig. 13. The idea is to build four large openings equally divided around the circumference within a few feet of the FIG. 13.erience trouble with scaffolding, etc., not due to a hot furnace, as described in Chapter X., page 75, they often resort to the use of more fuel than when all is working well. The additional percentage of fuel causes a greater heat, making the stock more plastic, and causing it to give way more easily from the walls of a furnace. It .generally takes from five to ten hours for stock to work down from the top to be tapped out as iron.