68 ANNUAL OF SCIENTIFIC DISCOVERY. 



serves the double purpose of reducing and calcining the ore. The fire is con- 

 tained in an ordinary fireplace situate at one end of the double furnace. 

 The gases and flame from this fire pass through a lateral opening or flue into 

 the reducing or flowing furnace, and, after passing over the surface of the ore 

 contained therein, enter by another opening or openings into the calcining 

 furnace, which is placed upon the same level, or nearly so, with the flowing 

 furnace, the gases passing off by a suitable flue or flues to the chimney. In 

 the passage or passages which conduct from the flowing furnace to the cal- 

 cining furnace there are placed suitable doors or dampers, which are so 

 arranged that by opening or closing certain of them, the gases or flame may 

 either be directed into the calcining furnace or cut off and turned intq a waste 

 flue leading to the chimney. 



Spence's Furnace for the Consumption of Smoke. In this furnace, invented 

 by Messrs. Spence & Sons, of Boston, the smoke and gases, when the 

 furnace damper is closed, are kept revolving directly over the fire in a large 

 dome, and can escape only through a tapering tube, the bottom of which is 

 very near the fire, and only one and a half inch in diameter. It is evident 

 there must always be a slight escape of smoke and gases to keep up a 

 draught to the fire ; but this tube, being so small in diameter, allows only 

 enough to escape to keep up the draught ; the remainder of the smoke and 

 gases is consumed. The power and economy thus gained are surprising. 



MACKENZIE'S BLOWING MACHINE. 



The blowers now in use are of two classes : the bellows and the fan. The 

 fan blower in various forms and proportions is driven at a high velocity, and 

 drives a large vclr.nie of air with a force sufficient for ventilating mines or 

 buildings, blowin- y the chaff in winnowing grain, or enlivening the 

 fires of a blacksmitn's open forge. But where the air is to be driven with any 

 considerable pressure or force, as in supplying divers at considerable depths 

 in the sea, or blowing blast furnaces for making iron, some form of the 

 bellows or of the pumping cylinder is almost invariably employed. The 

 interior of a blast furnace is filled some forty feet in height with a mingled 

 mass of ore, coal, and limestone, and the blast forced in near the base requires 

 a pressure of from one and a half to nine pounds per square inch to rise 

 through it. Fan blowers rarely yield a pressure of more than from three to 

 ten ounces per square inch, but the pumping cylinder may compress the 

 elastic fluid to any extent desired. The fan is, however, much smaller and 

 cheaper a fact which has induced an attempt to increase the pressure by 

 blowing from one fan into another, thus raising the pressure a few inches 

 with each lift. This is an English plan, and the effect observed was an 

 increase of pressure pretty nearly equal for each fan passed through. In this 

 country our blast furnaces are generally blown by pumping, and our cupola 

 furnaces, which require less pressure, by fans. 



Mackenzie's blower includes two cylinders placed eccentrically, one within 

 the other. The outer one is fixed, but the inner revolves, and hi doing so 

 protrudes blades or wings to such an extent as always to just wipe the 

 interior of the first. The ends being closed, and two liberal openings made 



