In early days blastfurnaces were very generally built singly, plants of two were scarce, and a greater number than that in charcoal practice were almost unknown. But as the world's consumption of iron has risen the number of furnaces per plant has increased almost as rapidly as the tonnage per furnace, there being two in the United States with eleven, many of six and seven, and only a small portion of the total furnaces are single furnace plants. This fact has modified the general design of plants fundamentally. It is obvious that when a furnace stands alone the different elements of the plant as a whole may be arranged in almost any relation to one another, but when two or more are grouped together it is plain that their raw materials should come in by a means of transportation common to all, and that their output should be similarly taken away. Also that labor can be saved by grouping certain components of the equipment of each furnace together, notably the blowing engines, boilers, and stoves. The first two can be supervised by the same men, and the third sometimes are. In considering the arrangement of furnace plants, therefore, we need scarcely to consider plants of less than two furnaces, because as stated above the equipment of the single furnace can be arranged in almost any reasonable way and meet the conditions fairly well.

On account of the enormous quantities of materials handled it is obvious that the best possible arrangement of the railroad tracks must be at the basis of any proper design, and all multiple furnace plants for many years past have virtually had the stock houses for all the furnaces continuous, all being served by the same set of tracks. These, for obvious reasons, are made straight except in rare circumstances, and should always be so. This virtually forces the furnaces to be built in a straight line parallel to these stock house tracks.

The next points in the design involving the handling of a heavy tonnage of material are the casting arrangements and the cinder pits, and here it took many years to reach a sensible design. Probably the greatest defect of all our designing is a tendency to put every part of the design either at right angles with or parallel to the next element, and plants have in general been laid out with their parts at right angles with or parallel to the other parts. The fact which seems to have escaped observation is that railroads do not run around right angles, and therefore with one part of the plant at right angles to another if the first were parallel with the tracks, the second must be at right angles to them, and therefore relatively inaccessible. In spite of this the line of the cast house was for many years built at right angles to the line of the stock house tracks, and in order to bring cars alongside the cast house to permit the direct loading of pig iron these tracks all had to make a sharp right-angle turn. Even worse is the fact that, as the curves must all be turned off in the same direction, they can turn to a tangent along the near side of the cast house wall, but can only approach it with great difficulty on the far side, a very disadvantageous condition.

A little careful consideration will show that there is no fundamental reason why the cast house should be at right angles to the stock house tracks, and when the first pair of Lorain furnaces were built an attempt was made to evade this difficulty by turning the cast houses toward one another, so making them parallel to instead of at right angles to the stock house tracks. This somewhat increased their accessibility, but took up much room, since obviously the two furnaces were more than the length of both cast houses apart.

Various modifications of the right-angle plan were used, but without reaching any design which met the conditions satisfactorily. When designing the plant of the Federal Furnace Company of Chicago, Julian Kennedy adopted a plan which will undoubtedly be more and more used, though often in modified form, as time goes on, he placed the line of the cast houses at a diagonal with the line of the stock house. Fig. 236 shows a ground plan of these works on which the names of the different parts are clearly marked so that the arrangement is easily comprehensible. It is obvious from this plan how easily all parts of the plant are reached by railroad tracks with short and easy curves, and it will be equally obvious on a little reflection that if the cast houses had been placed at right angles to the line of the stock house trestles, in the old-fashioned way, their far sides in particular would have been almost inaccessible to railroad tracks within the available yard limits.

A further development of this idea took place when the Gary plant of the Indiana Steel Company was designed. A small scale plan of this plant reproduced from The Iron Trade Review is shown at Fig. 237 (page 377). The scale is so small that some study is necessary to distinguish the different parts, but this can be done with a little pains.

In this case the cast houses were turned to an angle of about thirty degrees with the center line of the row of furnaces. The angle of the skip was made flatter and the base of the skip bridge further from the base of the furnace than in the Federal design so that tracks could be run along between the under side of the skip bridge and the founda-tion of the furnace itself, which greatly increases the accessibility of all parts of the plant to switching service. These tracks underneath the skip communicate with the other tracks in front of the furnace by ladder tracks between every second pair of furnaces, which run through diagonally on the same angle as that of the cast houses. These tracks serve not only the cast houses, but the dust discharges of the different dust catchers as well. In this case each pair of furnaces becomes a lozenge shaped island in a wide river of tracks, with practically every part of the plant within easy reach of at least one track. It is seldom wise to prophesy finality in any technical matter, but the general principle of this design is so nearly perfect that it seems likely that it will eventually come to be the only plan considered for multiple furnace plants, but, of course, modifications to suit individual conditions or changes in the component parts of the plant may be made in every case.