with the exception of the motion which its friction and the compression of the air occasions. When the machine moves from D (fig. 3) till the plane DC comes very near to the surface of the water \( w \), the valves \( q \) open, and a volume of air equal to the space DCS will be expelled through the cavity I (fig. 1), along the pipe P; during the time the valves in the cavity \( m \) (fig. 2) have opened to admit the same volume of atmospheric air on the returning stroke. The point B is carried the contrary way, by which another portion of air opens the valves \( t \) to pass through the pipe P, while the same volume of air from the atmosphere enters the cavity \( n \), which in its turn is forced through the exit valves \( t \).

The use of the swing valve MV will now be obvious. If it did not exist, every time the air was compressed on one side the water would be depressed on that side, and the compression of the air would be limited by the increased column of water on the other side. This valve, however, prevents the water from immediately changing its situation, no more escaping from one side of the valve to the other than what can pass between the edges of the valve and the cylinder, which, in the short space of one stroke, can be only a very small quantity. This may be considered as a great improvement upon the first machine, which we have before described. The patentee further intends occasionally to give to this swing valve a contrary motion to that of the cylinder, and thus still more to increase the blast. Or, in the use of a very small blast, the valve may be left at liberty, and used merely to prevent the too great agitation of the water, which in the original machine was considered as an objection. Two of those machines are frequently used together, and worked by cranks, forming an angle of 45° with each other, to make the strong part of the blast of the one to concur with the weak part of the blast of the other.

The part I of the exit pipe PI, must be precisely to the centre of motion. The part L works in a stuffing part, or a ground socket connected with the pipe LN. The latter should communicate with a regulator, which the patentee does not describe, but recommends one of water. This may be a vessel at least of the capacity of the cylinder, inverted in a reservoir of water, and may stand near to the bottom. The pipe N is inserted into the bottom, which is now uppermost. The height of the water in the reservoir must be such as to give the required pressure to the air.

When the air is forced into the inverted vessel by the machinery, the water descends in this, and rises in the reservoir, which now gives a pressure to the contained air equal to the difference of the height of the water in the inverted vessel and the reservoir. The surface of the reservoir should be the greatest possible, in order that it may be raised in the least degree by the water coming from the inverted vessel, which will have the effect of keeping the blast more uniform.

The water regulator is certainly the best for smiths' bellows, for refineries, forges, and perhaps the common melting furnace, but they have been found very objectionable in the blowing of large blast-furnaces. The air in the common blowing engine undergoes a great increase of temperature during its passage through the machine, often as much as 40 or 50 degrees. The heated air has the effect of carrying a greater quantity of water along with it into the furnace, which destroys a larger quantity of carbon than the same bulk of common air, without producing an adequate portion of heat. A great part of the heat of the air is doubtless produced by the friction of the piston of the blowing cylinder, which, in this construction, has a very tight wading. In the blowing machine above described, the water would doubtless be an objection in blast-furnaces, but, as its little friction Blowing would not heat the air like the common blowing cylinder Machines used in blast furnaces, the objection would be less formidable. Air must doubtless give out some heat by its decrease of volume, just as it will absorb the heat by rarefaction, as is experienced in exhausting the receiver of an air-pump. The converse of this is equally shown in the little instrument employed to kindle tinder by condensing the air within it.

The heat by the friction of this piston is probably much more than by the condensation of the air; the latter is obviated in the machine above described, and in another blowing machine lately introduced, of which we shall give a description.

This machine, in its general appearance, does not seem to have any advantage over the common blowing cylinder, but in practice it is found superior.

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 parallelopipedon. A board is made to fit pretty nearly its cross section, 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 admit air, and at the same end is a pipe with a valve opening outwards.

The machine above alluded to as having some resemblance to this, is the invention of Mr Vaughan, who has fitted up several of them for foundries, and they are much approved. The writer of this article took a drawing from one of these machines employed to melt cast-iron at the Phoenix Foundry in Sheffield.

Figs. 6 and 7 are two views of the machine. ABCD is a square box formed of pieces of cast-metal, screwed 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 \( w \) by the spear G, which communicates with the crank of a wheel at a distance.

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 half an 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, \( v \) and \( n \), are cut diagonally, in order to place the pieces of leather, \( l \), between them. These leathers, with the wood, are firmly fastened to the plate by bolts, such as \( g \).

The leathers extend about two inches beyond the wood; and their slight elasticity keeps them in contact with the metallic surface, which is not required to be very smooth. When the piston moves towards the end of the box, to which the leather projects, the leather claps close to the surface, rendering 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 contained 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 produce a sufficiently uniform blast for any purpose.

When the leathers of the piston are rubbed with black lead, the friction amounts to almost 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 applied 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 2½ inches in diameter. When the length of stroke is the greatest, 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 beat 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 required. In their improved state they may be employed for most purposes.

All the calculations relative to bellows will be easily made, by the following rules and formula:

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, whether by a column of water or by a weight, call p.

v = the velocity with which the air escapes.

r = the resistance, in pounds, which the blast will give.

Then cn = q, the quantity discharged in one minute, and v = \(\frac{cn}{a}\) in one minute, or \(= \frac{cn}{60a}\) for 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, \(\frac{v^2a}{32 \times 14} = p\); the weight of 14 cubic feet of air being equal to one pound.

The energy of air in blowing fires is as the quantity, 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 to iron-masters. For a description of the more recent and improved method of blowing, see IRON-MAKING, and SMELTING.

(c. s.—ft.)