Page:Popular Science Monthly Volume 38.djvu/160

148 the heap was of the desired height; the outside of the mass of charcoal and ore was then incased in a covering of rough stones laid in a mortar of clay and sand, or, in some cases, it was merely plastered over with a thick layer of such mortar; care was always taken to have a hole near the bottom, just above the edge of the hearth, for the insertion of a tube of baked clay to serve as a tuyère, and a second hole at the top for the escape of smoke and gases. Fire was then introduced at the tuyere and the bellows connected; a gentle blast being used until all the moisture in the ore and the covering of the heap was driven off. As soon as this was accomplished, the blast was increased and the heat thereby augmented. At the end of several hours a mass of metallic iron, weighing twenty or thirty pounds, was found in the bottom of the hearth, from which it was removed by tongs and forged by sledge-hammers into the desired shape, several reheatings being required. The iron obtained was not usually over twenty per cent of that in the ore, and only the richest ores were used.

The first attempts to smelt iron-ore were probably made in open, or perhaps partially inclosed, fires, in which the operation was conducted without the stimulus of a blast; but the slow and very irregular burning of the fuel during calms, as compared with its more rapid and effective combustion when urged by a high wind, must have soon suggested the desirability of a regular and manageable method of supplying the primitive furnaces with a current of air, and we find that the use of some contrivance for this purpose is of great antiquity.

Bellows are known to have been used by the Egyptians over three thousand years ago. They consisted of a pair of leather bags (which were nearly spherical when inflated), to each of which was attached a tube for the discharge of the air. The operator stood with a foot on each of these bags, and pressed them alternately by throwing his weight from one foot to the other. In the top of each bag was a round hole, which could be closed by the foot of the workman, and a cord held in each hand enabled him to distend and inflate either bag as he compressed the other. His feet served as valves to prevent the escape of air from the holes, and compelled it to pass through the discharge-pipe into the fire.

Piston bellows were known in Egypt at least two thousand years ago, and compressed air was used for various purposes other than blowing fires. The kind of bellows shown in Fig. 1 was known and used by the Greeks and Romans at a very early period, and the bellows of our kitchens are of equal antiquity. Bellows