BELLOWS. Some form of bellows was probably the earliest form of blowing-machine. A very primitive form of bellows is still in use in some Eastern countries, consisting simply of the skin of some animal sewed into a rude bag, with a valve and nozzle. The older forms of domes tic bellows are all constructed on the same prin ciple—viz. a chamber formed of two boards with flexible leather sides, having at one end a nozzle with a narrow mouth ; and in the lower board a valve of considerably larger area for the admis sion of air. When the bellows are distended by drawing the boards apart, air is sucked in by the valve, to replace the vacuum which would otherwise be farmed, and then, when the boards are being closed. the valve, which only opens inward, is shut by the compressed air; and the latter, having no other escape, is forced out at the nozzle. The great fault of the common bel lows is that it gives a succession of puffs and not a continuous blast. A former remedy for this was to use two bellows, so that one was blowing while the other was filling; but it was afterwards found that the double bellows secured a still more uniform blast. This machine is merely the common bellows. with a third hoard
of the same shape as the other two placed be tween them. so as to form two chambers instead of one. The middle hoard is fixed, and both it and the lower one have valves placed in them opening inward. A weight on the lower board keeps the under chamber filled with air; and when this board is raised by a lever or other wise, the air which it contains is forced into the upper chamber. The exit-pipe is attached to the latter, and a weight is placed on the upper board sufficiently heavy to press the air out in a con tinuous stream, the continuity being maintained by the large quantity of air always present in the upper chamber, and the uniform pressure of the weight. Sometimes a spring is used instead of a weight to press out the air. This is the usual construction of the ordinary blacksmith's bellows. Even with the double bellows, however, the constant refilling of the upper portion from the lower prevents the blast from being quite regular. and its use is therefore limited to such simple requirements as are furnished by black smiths' forges and domestic fireplaces.