BLOWING ENGINE, is a machine for forcing air with great velocity into a furnace in order to increase the combustion and is now used in all the practical operations of metallurgy.
The machine first employed for this purpose was a pair of leather bellows wrought by the hand; but when it became necessary to smelt iron in large quantities, the size and number of the bellows were increased. Two pairs of bellows were so connected by means of a le ver, that the one pair shut when the other opened. The handle of each pair was successively moved by two cogs, placed at right angles to each other on the horizontal axis of a water wheel ; so that during the revolution of the wheel, one of the cogs shut one pair of bellows, and forced the included air into the fur nace, while the other, which was at this instant open ed, was shut by means of the other cog, and thus discharged its contents into the furnace. By this means a continued blast is kept up, excepting a trifling pause when the motion is changed. A ma chine similar to this, called the slag-mill, is used for refining the lava from the reverberating furnace in which lead ore is smelted.
Another engine, called the water blowing machine, has been used for producing a strong blast. It has been pretty generally adopted on the continent-for more than a century, but does not seem to have come into use in this country. A current of water is made to pass through a kind of cullendar placed in the open air, and perforated with a number of trian gular holes. The water descends through these apertures small streams, and by exposing a great surface to the atmosphere, it drags along with it an immense quantity of air, and is conveyed through a tube till it dashes against a stone pedestal inclosed in a large vessel. The mixture of air and water which falls upon the pedestal is dispersed in every direction ; the air is separated from the water ; it ascends to the upperpart of the vessel, and rushes through a pipe to the furnace, while the water de scends ti:rough apertures at the bottom of the vessel.
Fabri and Dietrich imagined, that the wind is casioned by the decomposition of the water, or its transform? 'ion into gas in consequence of the agita tion and percussion of its parts ; hut M. Venturi, (Experimental Inquiry concerning the lateral com munication of motion in Fluids, Prop. VIII.) to whom we are indebted tor the first philosophical ac count of this machine, has shown, that this opinion is erroneous, and that the wind is supplied from the at mosphere ; for when the lateral openings were shut, no wind was generated.
Hence the principal objectin the construction of these machines is to combine as much 'air as possible with the descending current. With this view, the water is often made to pass through a cullendar, as al ready mentioned.
Franciscus Tertius de Lanis, (Magistero Nat. et Ar tts, lib. v. cap. 3.) observes, that he has seen a greater wind generated by a machine of this kind, than could be produced by bellows ten or twelve feet long.* Machines of such a nature might have been suffi cient for smelting iron when charcoal was used for fuel as in other countries ; but when coal began to be used; it became necessary to construct machines capable of affording a powerful and constant • blast, and formed of the most diirable materials.
The earliest contrivance of this kind was a forcing pump, worked by a water wheel, or a steam engine ; and it would appear, that the first cylinders of this kind, at least those of any magnitude, were erected by Mr John Smeaton, in 1760, at the Carron iron works. • The pumps were wrought alternately by a water wheel, having four cranks upon its axis, each of which moved the piston of a cylinder, which had a stroke of four feet six inches ; the diameter of each cylinder being also four feet six inches.
In situations where a fall of water could not be obtained, steam engines were employed to work the pumps ; but as these machines were then only single, the piston descending by the pressure of the atmo sphere, it was'necessary to have some contrivance for producing a continued stream of air during the de scent of the piston. This object was effected, by re ceiving the air into a regulating cylinder of the same size as the blowing cylinder, and furnished with a piston loaded with heavy weights. As every stroke of the engine would pump into this cylinder twice the quantity of air that would pass through the nose pipe into the furnace in the same time, the air raised the loaded piston of the regulating cylinder, and du ring the time that the engine ceased to act, the weight of the regulating piston forced the air' into the • fur nace. This method of regulating the blast, which continued in general use for many years, has been superseded by the water regulator, and by the dou ble acting blowing cylinder, wrought by a Steam en. gine of Watt and Boulton's construction.