58 METALLURGY OF CAST IRON.
top of the stack. These are connected with flues branching upward about eight feet high, and closed by means of valves hung on pivots, as seen at H H, and so regulated by weight that they will open of themselves when any excess of pressure is created in the furnace. This improvement is a step forward in furnace practice which diminishes the risks of accidents and loss of life, but it still remains to better guard against the evils of scaffolding or the slipping of stock so detrimental to successful furnacing, often requiring several days after a slip to get a furnace back again to working satisfactorily and give a fair uniform grade of iron.lieve 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