We are indebted for the illustrations and the particulars to Dr. Percy's invaluable book on iron and steel (probably it is not saying too much to describe it as the best work on the subject ever written).
SECTION OF INDIAN BLAST FURNACE AND BLOWING MACHINE.
Fig. 1 shows a sectional elevation, and Fig. 2 shows a plan of furnace and bellows and tuyeres, indeed, an entire ironworks plant used in India, not only now, but, so far as we can gather, from time immemorial. The two figures give a sufficiently clear idea of the form of furnace used in Lower Bengal, in which portion of our Indian empire there are entire villages exclusively inhabited by iron smelters, who, sad to relate, are distinguished from the agricultural villages surrounding them by their filth, poverty, and generally degraded condition. There are whole tribes in India who have no other occupation than iron smelting. They, of course, sink no shafts and open no mines, and are not permanent in any place. They simply remain in one place so long as plentiful supplies of ore and wood are obtainable in the immediate vicinity. In many cases the villages formerly inhabited by them have passed out of existence, but the waste, or rather wasted products, of their operations remain.
The furnace shown in Figs. 1 and 2 is built of the sandy soil of the district, moistened and kneaded and generally strengthened by a sort of skeleton of strips of flexible wood. In form it varies from a cylinder, more or less circular, diverging into a tolerably acute cone, the walls being about 3 in. thick. The height is generally about 3 ft. and the mean internal diameter about 1 ft., but all these dimensions vary with different workmen and in different localities. There are two apertures at the base of the furnace; one in front, about 1 ft. in height, and rather less in width than the internal diameter of the furnace, through which, when the smelting of one charge is finished, the resulting mass of spongy iron is extracted, and which during the smelting is well plastered up, the small conical tuyere being inserted at the bottom. This tuyere is usually made of the same material as the furnace - namely, of a sandy soil; worked by hand into the required form and sun-dried; but sometimes no other tuyere is employed than a lump of moist clay with a hole in it, into which the bamboo pipes communicating with the bellows are inserted.
The other aperture is smaller, and placed at one side of the furnace, and chiefly below the ground, forming a communication between the bottom of the furnace chamber and a small trench into which the slag flows and filters out through a small pile of charcoal. It is this slag being found in places where iron is not now made that shows that iron smelting was an occupation there, perhaps many centuries before.
The inclined tray shown at the top of the furnace on Fig. 1 is made of the same material as the furnace itself, and when kneaded into shape is supported on a wooden framework. On it is piled a supply of charcoal, which is raked into the furnace when required.
The blowing apparatus is singularly ingenious, and is certainly as economical of manual labor as a blowing arrangement depending on manual labor well can be. A section of the bellows forms the portion to the right of Fig. 1, showing tuyere forming the connection between bellows and furnace. It consists of a circular segment of hard wood, rudely hollowed, and having a piece of buffalo hide with a small hole in its center tied over the top. Into this hole a strong cord is passed, with a small piece of wood attached to the end to keep it inside the bellows, while the other end is attached to a bent bamboo firmly fixed into the ground close by. This bamboo acts as a spring, drawing up the string, and consequently the leather cover of the bellows, to its utmost stretch, while air enters through the central hole. When thus filled, a man places his foot on the hide, closing the central hole with his heel, and then throwing the whole weight of his body on to that foot, he depresses the hide, and drives the air out through a bamboo tube inserted in the side and communicating with the furnace. At the same time he pulls down the bamboo with the arm of that side.
Two such bellows are placed side by side, a thin bamboo tube attached to each, and both entering the one tuyere; and so by jumping on each bellows alternately, the workman keeps up a continuous blast.
Fig. 2. - PLAN OF INDIAN BLAST FURNACE AND BLOWING MACHINE.
The Figs. 1 and 2 are taken from sketches, and the description from particulars, by Mr. Blandford, who was for some years on the Geological Survey of India, and had exceptional opportunities in his journeyings of observing the customs and occupations of the Indian iron smelters. The blowing machine is an especially wonderful and effective machine, and was first described and illustrated by Mr. Robert Rose, in a Calcutta publication, more than half a century ago. He also had seen it used in iron making in India. - Colliery Guardian.