BLOWING-MACHINES, in the arts and ma nufactures, and in domestic economy, are instru ments for producing a continued current of air, prin cipally for the purpose of facilitating the combustion of fuel. The first idea of such a machine was doubt less derived from the lungs, which we are constantly in the habit of using for the purpose of blowing, but more especially in the simple and useful application of the blow-pipe.
Of these different machines, the common bellows r bears the greatest resemblance to the lungs, and was, 1 in all probability, the first contrivance for artificial blowing. In the first instance, this instrument might be a simple bag, capable of distension by a mechanical force, the air being drawn in and pressed out of the same aperture in the manner of breathing. The first improvement upon this simple form would be, to ad mit the air. by a valve opening inwards when the bellows were distended, the blast outwards being .
from another aperture. This improvement consists in the air being admitted at a wider aperture, which fills the bellows in less time than would be perform ed through the small pipe through which the air should escape. The blast, in this state of the ma chine, is not continuous, but in puffs, at intervals of time required for the air to enter the bellows through the valve ; the blowing interval being to the filling interval as the areas of the apertures. This irregu lar blast was for some time remedied by employing two bellows which blew alternately, the blowing on one taking place while the other.was filling. This inconvenience was but partially remedied by this contrivance. The invention of what are called dou ble bellows must have been considered a valuable ac quisition in the art of blowing. Previous to describ ing these, it will be necessary to give a description of single bellows above mentioned.
It will be needless, however, to say more than re fer the reader to common domestic bellows, which are in every respect the same as the single bellows first used. The leather nailed to the upper and lower boards is prevented from collapsing, when the boards are separated by a hoop of wood contained within, performing the office of the ribs in the ster num of animals, without which the breathing would not be performed. The lower board contains the
valve which admits the air. When the two boards are separated, the air lifts the valve in entering the cavity. When full of air, the closing of the boards causes the air within to close the valve to prevent its return in that direction, and compels it to escape at the pipe, the mouth of which is called the nozle or nose-pipe.
In order to conceive the construction of the dou ble bellows, we have only to take a third board ex actly of the shape of the other two, and connect it with the lower board by a piece of leather similar to that of the single bellows, making two cavities ex actly similar, and separated by the lower board of the single bellows, which now becomes the middle board of the double bellows. The third board we shall now call the lower board. This latter has a valve in it exactly similar to the first, which still re tains its place in the new construction.
The middle board is now fixed in a horizontal po sition, the pipe being placed to the fire to be blown. The lower board is held down by a weight, which keeps the lower cavity constantly full of air. The top board has a weight laid upon it which presses all the air out of the upper cavity through the pipe.
The machine! action by which the blowing is per formed, is, first, to lift up the lower board. This forces the air from the lower into the upper cavity, the valve in the middle board preventing its return. The weight on the upper board now presses the air with a uniform blast through the pipe. During this time the lower board descends, which fills the lower 'cavity with air from the atmosphere. This again rises, and gives its contents to the upper cavity, and thence through the nose-pipe. Hence we see that irregular puffing blast which belongs to the single bellows is here confined to the lower board only, which sup.