In addition to the apparatus previously described which is required for each furnace there must be a considerable amount of other equipment for the plant as a whole.

It goes without saying that the enormous tonnages involved at modern blast-furnaces can only be handled by first-class railroad track and equipment, both of cars and locomotives, and in sufficient numbers, and that at practically all plants of any size cranes are extensively used for handling heavy parts, cleaning up "messes," and doing innumerable kinds of work that were formerly done by hard manual labor. Very frequently they are arranged to operate grab buckets and magnets, as well as serving for general utility cranes. These are all standard equipment and do not need to be specially described here.

The Water-Supply System

The water-supply system is one absolutely indispensable portion of the equipment which, to judge by the location and the design of some plants, was forgotten at the time of their construction and then put in as an afterthought.

The modern furnace depends upon water-cooling for its very existence, not from minute, to minute, but literally from second to second, since the tuyeres, coolers and cooling plates are exposed to the most intense heat and the severest conditions of scouring by iron and slag, not occasionally, but in many cases continuously, and only a thin surface of the highest possible conductivity cooled by a violent circulation of moderately cool water prevents their instant destruction.

For this purpose water in considerable quantity must be provided. Its quantity varies very greatly with the size of the furnace and the method of cooling adopted. Cooling plates require more than bosh jackets, and, of course, when cooling plates are used above the mantle they add their quota to the total requirements, since a certain minimum velocity must be maintained for each plate, the minimum depending upon the temperature to which the plate is exposed. For an ordinary 500-ton furnace from 1200 to 2000 gallons of water per minute are required for cooling the tuyeres, hearth and bosh.

In addition to this the water necessary for boiler feed, and very generally for condensers, must be supplied, and in modern practice great quantities are being used for gas washing also. This amounts to about 4 gals. for primary cleaning for every 100 cu. ft. of gas or about 2000 gals. per minute if all the gas is washed. It should be noted that the furnace cooling water can be and generally is used over for either condenser or gas cleaning. The consequence is that each blast furnace requires a very respectable volume of water, from 3,500,000 to 6,000,000 gallons per day, and a plant of several blastfurnaces needs a supply which makes that of many large cities look small in comparison.

Plants have too often been designed with little or no consideration for their location in regard to water supply. There are perhaps more important considerations, such as the arrangement of tracks, etc. -but in a number of cases that have fallen within my own experience a location close to the water supply would have been not only as good but better in other respects than the location actually chosen, at some distance from it, with the necessity of long lines of communication and long-distance supervision of the pumping plant, for, of course, in modern practice long suction pipes are rightly not tolerated, and the pumping plant must be close to the water supply and within a moderate distance above the water level. Moreover, the pumping plant must be able to run and supply water to the furnace irrespective of fluctuations in the height of the supply. These conditions are easy to fulfil if the plant be on the border of a lake or a stream whose level does not greatly fluctuate, but very difficult to meet in some cases where the source of the water supply is a stream with a rise and fall of many feet, such, for instance, as have the Monongahela and Ohio rivers in the Pittsburgh district.

The design of the pumping station must be based on the local conditions and on the size of the plant. Where a very large plant is needed on the banks of such a river it is often desirable, if not necessary, to sink a huge caisson down below low water level from a point high enough above the river level to be out of danger of floods, and run a tunnel of brick or concrete from this out into the river itself. This, of course, requires a cofferdam of some extent for the construction of the tunnel.

The pumps are located at the bottom of the caisson or pit and the flow of water into it is controlled by valves at the inner end of the tunnel so that no matter how high the river may rise the pumps cannot be drowned out.

The screening of the water is done in the pit, no attempt being made to erect screens over the mouth of the tunnel since they would be inaccessible in times of flood.

In other cases a masonry forebay is built at the bank of the river extending well down below water level, its front being entirely open to the river except that it is guarded by screens. These may either be fixed or arranged to be removed for cleaning. The latter, of course, can only be done by having two separate chambers both of which can be entirely cut off alternately, or by having two sets of screens, one in front of the other so that each one alternately can be raised for cleaning. The possible variations of these methods are of course almost infinite, and the choice of the best one is of great importance because the water supply of furnaces is more apt to be interrupted by floods than by any other kind of accident whatever. The likelihood of dangerously low water can be foreseen, and the necessary arrangements for an additional supply made in ample time, but when a flood arises, especially in a mountainous country, two or three hours may see a change from placid operation to one of absolute disorganization on account of water supply. This is for the reason that when these violent floods occur the water picks up vast quantities of silt, leaves, and sticks, so that its consistency is almost like soup, in extreme cases, and this combination can stop up a screen in a short time almost as effectively as could a plasterer, while owing to the location of the screens it is not always possible to clean sufficient of their area to let through the water necessary to the life of the plant.