This is the most important single step in the whole iron-making process. The details by which it was carried on in early years are quite unknown to me. The earliest system of which I have knowledge consisted in throwing into the open furnace top the ore and limestone from large wheelbarrows, while the charcoal was thrown in from baskets made for that purpose, these baskets being elliptical in shape, about 4 ft. long by 2 1/2 ft. wide by 1 ft. deep, with hand-holds at each end. When mineral fuel was used it was handled in wheelbarrows, and even before the introduction of the closed top the use of "filling-barrows" became almost universal except at charcoal furnaces. These barrows are the two-wheeled type illustrated in the last chapter.

Fig. 25. Single bell and hopper.

The first method adopted for closing the top of the blast-furnace was the one which has remained in use practically ever since. The apparatus is known as the "bell and hopper." In its simplest form it is illustrated by Fig. 25. It consists of an inverted cone forming a hopper set on, or in modern practice, fastened to the top of the furnace, the opening of the hopper being closed by a cone which sometimes has a rounded top and from its general shape takes its name, the "bell." The bottom edge of the hopper is turned true in a boring mill as is the lower portion of the surface of the bell, so that they make a good fit. Into the annular space of triangular section formed by these two, the charge is dumped, by tipping forward the barrows on their own axles as a center, then when the bell is lowered, the charge slides into the furnace through the annular opening formed.

During the long period in which the furnace was approximating its modern development, ending with the Duquesne revolution, this method of filling was almost universal.

The quantity of labor it involved was well recognized, and many efforts had been made to avoid this by the introduction of mechanical methods of charging; but these have almost universally had a highly detrimental effect on the operation of the furnace, so that in earlier times they were soon abandoned for the time-tried method universally known as "hand-filling".

It seems at first sight absurd that so simple a matter should be so obscure and should involve such great difficulties. But the spacing of the stock on the bell, the dumping of the barrows at the edge of the hopper, or on the apex of the bell, the size of the charge, and whether the ore and stone should be dumped with the coke, or separately, are all questions which may exercise an influence on the working and economy of the furnace so great as to be literally vital.