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TAPPING-OUT AND STOPPING-UP FURNACES AND CUPOLAS.
It has taken much time, study, and experience to attain the present perfection in controlling the output of a modern furnace. The history of blast furnaces shows many disasters in " breakouts," " boils," and explosions. When all is working well about a furnace everything seems very simple and as if taking care of itself, but it is when all does not go well that one is impressed with the fact that furnacmg is often more like hades let loose than a paradise of comfort, ease, and pleasure. An observing founder standing at a distance watching a furnace being tapped might often be at a loss to understand why a cupola cannot have its " breast'' stopped the same as the ' * notch " of a furnace. The founder often has trouble with cupola tap-holes, which when once started to work badly will often continue to do so throughout the balance of the heat. The secret of the furnaceman being able to stop a notch by hand in the way it is generally done, is that the metal, when all is working well, is left lower •than the notch-hole, about as illustrated at the level O, Fig. 18, page 90. How the metal goes down to such a low level as shown, is a puzzle to the founder who hashich convey the hot blast to the furnace are either coated with an asbestos covering or have their interior lined with fire brick, the same as is done with the " down-comer " which carries the dead gas from the top of the furnace down to the combustion chamber of the hot blast stoves to protect them and prevent loss of heat.gathers on the combustion chambers for a distance of about twenty feet in height, and on the bottom of the stoves, which have openings as at K and H for getting at or cleaning out the stove, or, if shut off, for repairs.d checkered brickres, etc. It may also beency :|,