The construction shown by Figs. 162, 163 and 165 in which the mantle is supported directly upon the tops of the columns, numbering in modern practice from ten to twelve, has virtually been the standard ever since the adoption of the steel-shell construction, but is open to various objections from a practical and operating point of view.

These objections are that the columns come very close to the walls of the bosh and particularly to the outside of the hearth jacket, narrowing up the cooling ditch around the base of the latter and making the removal of any iron which may run into the ditch in a breakout extremely difficult, because this iron locks itself between the hearth jacket and the columns and in some cases cannot be removed without blasting, which would endanger the columns themselves. Moreover, when this construction is used, the bustle pipe carrying the hot blast to the tuyeres has to pass outside the columns, and the penstocks, carrying the hot blast from the bustle pipe to the individual tuyeres, have to pass between the columns. These penstocks have to be swung out of the way whenever the tuyeres have to be changed, and the columns are greatly in the way at such times. There is nearly always a column close to the tuyere on one side or the other and access to' the tuyeres is enormously hindered thereby. These columns interfere with the lead of the individual water pipes from the circular water main beneath the bustle pipe to the tuyeres and cooling plates and make it difficult to determine which cock controls which pipe, a matter of vital importance in case of a partial obstruction to the flow in one of these pipes, which then requires instant attention as the price of preventing the destruction of the cooling member that it supplies, and the stopping of the furnace to replace the latter.

The writer having realized for years past the seriousness of these difficulties from an operating point of view, when the charcoal furnace at Ashland, Wis., required reconstruction a few years ago, designed it along somewhat different lines, which are shown in Figs. 167 and 175. The central idea of the construction adopted is to remove the columns from their ordinary location immediately under the mantle and set them back far enough out of the way to give complete access to the base of the furnace and to prevent injury to the columns themselves in case of breakouts or other accidents around the furnace.

This was accomplished by building a square framework of extremely heavy plate girders, the inside distance apart of which was slightly greater than the outside diameter of the shell of the furnace. These girders were supported on the top of the four columns to which they were riveted and strongly braced to prevent the possibility of failure by rotation of the structure about its vertical axis. The shell was supported on these girders by eight brackets, two on each girder, these brackets being heavily riveted to the shell.

In order to prevent the sagging of the mantle plate eight cantilever brackets projected in under the mantle, one vertically under each of the main brackets. These were supported by a downward extension of the main angles which fastened the main brackets to the shell and the outer ends were held down by struts extending down from the ends of the main brackets.

The construction was a success in all respects and gave a degree of accessibility and convenience in operation around the bottom of the furnace beyond comparison greater than that of any other type. This accessibility is indicated by Fig. 175, which shows two men abreast, standing shoulder to shoulder inside the column, and outside the outermost point of the penstock. Of course, the tuyeres do not come in line with the columns in this construction any more than in the ordinary one.

Fig. 175. Ashland construction.

For a furnace of this size no change in the design of the construction need be made. For a coke furnace of greater size and with greater liability to serious difficulties of operation, it would probably be desirable to use five columns, so that if one of them were to fail three of the girders, encircling more than one-half the furnace, would still stand and support it. This, of course, would only happen in case of a terrific disaster because the columns are set back so far from the furnace that no ordinary accident could affect them, and on account of the abundant room around them they can be thoroughly protected by brickwork, In case this construction were used for a coke furnace a box girder would be used instead of the single plate girder and this box girder would be made water-tight and serve for the circle pipe to supply cooling water around the furnace. This would prevent any possibility of the girders being softened or affected by heat no matter what happened.

This construction permits the bustle pipe to be put inside of the columns and thus to have the penstocks as close to the tuyeres as may be desirable without having any interference between the penstock and the columns. This also shortens up the bustle pipe materially, which reduces both its weight and its cost. One of the important features of this construction when used to replace the standard type, is that the foundations, lying entirely outside those of the old construction, may be put in while the latter is being torn out, and the structural work may be erected before the old furnace is down, as was done in the case illustrated, with the saving of many weeks in time, worth many thousand dollars more than the slight additional cost of construction.