It resembles in some degree the common smith's bellows of the Chinese, which consists of a square wooden trunk, in the form of a parallopipedon. A board is made to fit its cross section, pretty nearly, to which is attached a long rod by which the board is pushed backwards and forwards like a piston. At one end of the trunk is a valve opening inwards to ad mit air, and at the same end is a pipe with •a valve opening outwards The machine above alluded to having some resem blance to this. is the invention of a Mr Vaughan, who has fitted up several of them for founderies, and which are much approved. The writer of this ttr tide has tam a drawing from one of these machines employed to melt cast-iron at the Phoenix Foundry • in Sheffield.
Figs. 6. and 7. are two viewsof the machine. ABCD is a square box formed of pieces of cast metal, screw .
ed together by hinges. Two of these are placed side by side, as may be seen in the end view, fig. 7. MQ is a piston fitting the square box, which is drawn backward and forward by the rod EF, which works horizontally on the wheels tvz by theG, which communicates with the .crank of a at a dis stance.
The piston MQ, which is the most ingenious part of this machine, is enlarged in fig. 8. to render it clearer. The body of the piston is a cast-iron plate about one-half inch thick, with a socket in the middle to receive the rod. The diameter of this plate is about one-fourth of an inch less than that of the box. Two pieces of wood, v *, are cut dia gonally, in order to place the pieces of leather, 11, between them. These leathers, with the wood, are firmly fastened to the plate by bolts, such as g This leather extends about two inches beyond the wood : their slight elasticity keeps them in contact with the metallic surface, which is net required to • be very smooth. When the piston moves towards the end of the box, towards which the leather pro jects, the leather claps close to the surface, render ing it air-tight, while the leather on the other side of the piston becomes loose, and has no friction. These leathers will be contrarily acted upon, when the piston acts the contrary way. The projecting curved pipes, HI, form a communication between the box where the piston works, and the air-chest N. When the piston moves from B to D, the valves F and V open, while L and S are shut. The air con tained in the box is now forced through the valve R into the chest N, and from thence along the blast pipe P.
In the returning stroke, which is the whole length of the box, the valves R, V, and K, are shut, while L and S open. The air is forced through H to N) and then through P.
Two of these work at the same time by two cranks, which cause one to be in full blast at the time the other is returning the stroke; so that, with due management, the four puffs produced by two double strokes may be made to succeed each other at equal intervals, which almost amounts to a steady blast. The inventor recommends four of these
boxes all to work together, which would produce eight puffs in the time of one double stroke, which, if divided into equal intervals, would prpduce a suf ficiently uniform blast for any purpose.
When the leathers of the piston are rubbed with black lead, the friction almost amounts to nothing. The leather acts so easy to the surface, and is so flexible, that it may be very easily raised with the fingers. This could not be the case, if it were ap plied in the same way in a cylinder ; and this is a sufficient reason for using the square box instead of the cylinder.
This machine makes 70 strokes in one minute ; the nose-pipe, where the blast enters the furnace, is 2_1_ inches in diameter. When the length of stroke is the greaten, at the above speed, it furnishes about 1200 cubic feet per minute.
This machine steers clear of the objection of the water, and, from its small friction, will have less tendency to heat the air. Its original cost is also less than any other machine yet constructed. In the situations where it has been adopted, it gives the highest satisfaction. The first construction of Street's bellows, above described, was only fitted for some smiths' fires, where a very soft blast was re quired. In their improved state they may be ens. ployed for most purposes.
All the calculations relative to bellows will be easily made, by the following rules and formals : First, get the space or capacity formed by one stroke of the machine, call this c, cubic feet.
Then get the number of strokes per minute, which call n.
The area of the nose-pipe, in feet, call (a).
,The pressure on the air to be discharged, whe ther by a column of water or by a weight, call p. v= the velocity which the air escapes with.
r.-= the resistance, in pounds, which the blast will give.
Then cn =f the quantity discharged in one tai en nute ; and v = ns a — in one minute, or -- for a 60 one second.
Then since the resistance is equal to a column of the fluid of the area a, and twice the height to give the velocity, v p. The weight of 14 82X 14 cubic feet of air being equal to 1 lb.
The energy of air in blowing fires, is as the %loan tity, and inversely as the space it occupies. For if the same quantity of air be consumed in half the space, the intensity of the heat, or the temperature of that particular place, will be double. Hence it is found, that the same quantity of air, by weight, in winter, will produce a greater. effect on a blast furnace than in summer, merely from the difference of density. The great difference in produce of iron in the cold and hot seasons of the year, is a fact notorious with iron masters. (T.)