These blowing-machines are also found to an swer very well for melting cast-iron, the soft blast having less tendency to destroy the carbon the quantity of air being compensated by increasing the aperture.
One of these machines is the invention of Mr Street, for which he has taken out a patent. It con sists of a barrel-shaped vessel, from 4 to 5 feet in diameter, and of a length more or less proportionate to the work it has to perform.
This cylinder is supported on two bearers by the two ends of its axis li6 a barrel churn. The cylin der is divided into two equal parts by a plane in the direction of its length, fitting the two ends and the upper side, water-tight, and extending downward to a small distance from the opposite side. This sep tum is in a perpendicular position when the cylin der is at rest. When this partly filled with water, and is made to pass through a certain space on its axis, the air which occupies the upper part of the vessel ;n11 be compressed on one side by the wa ter, which flows from one side of the septum to the other, and will become in the roe degree raided on the other, from a contrary cause. 14 however, in this situation, a valve be made to open inwards from the atmosphere on the rarified side, and ano ther to open outwards on the condensed side, two equal and contrary currents will be established, one inwards, and the other outwards. On the returning stroke both these valves will shut, and the other two sides will be put in the same situation with the first cavities. If, now, two similar valves to the last be introduced, two similar currents will be produced. If the two valves at which the air escapes from the machine, one on each side the septum, be made to communicate with one cavity from which a nose. pipe proceeds, while the other two valves commit. Blade with the asmosphere, every stroke will dis charge a quantity of air through the nose-pipe from one cavity, and introduce the same volume of sin from the atmosphere into the other cavity. These strokes are produced by the oscillating motion of the machine, the limit of its vibrations being about a quarter of the circle or goo.
These alternate puffs of air'are first propelled into a vessel containing water to regulate the blast. This vessel is divided into two portions by a septum, which passes from the close cover at the top nearly to the bottom. When the air is forced into the ea.
vity, which is close at the top, it expels the water under the septum at the bottom into the open cavity, so as to keep a constant head in the latter, compress. ing the air in the former. From this air-chest, a nose-pipe proceeds to the fire, and the air escapee from it with a uniform velocity so long as column of water in the chest is preserved. This de, scription answers to the first machine of the inven tor ; he has since taken out a second patent ; the specification of which is given in the fivosibo ry of Arts, Vol. X.XVIII. p. 198. • We than here give a description of this machine, with the tee's improvements. See Plate XXXV. figs. 1, $, and 8.
Fig. 1. is a longitudinal section of this machinek AB is the cylinder resting upon the axis do and cd, which are supported on the uprights gg. The esca lating motion is given to it by a rod working upon the pivot p, the other end of which is connected with a crank of such a length as to cause the cylinder to move through an arch of 90 degrees. The vessel is filled with water to the height ter.
The part CBD (fig. 2.) is cut off from the rest of the cylinder by two planes meeting at c, and conti nuing down to the axis r, so as to work upon its convex surface. These planes extend the whole length of the cylinder, and are then divided trans. versely into three cavities GHI, as seen in fig. 1. The cavity G is for the reception of the external air, and la called by the patentee a receiving box. The cavity H is open to the atmosphere, the periphery of the cylinder being removed in that part. The cavity I is appropriated to the air- which I. driven out of the machine, through the valves tt and qg (fig. S.), which open alternately on each side. The cavity G is divided longitudinally in the middle, forming two cavities, es and a, fig. 2., two valves, e and f, fig. 1.9 open late each, Ems best the end of the cylinder, • and the other from the cavity H. Each of the ca vities m and * communicate with the body of the cy linder by the holes kh in the dividing planes. The cavity I has no division, as it receives the air from both sets of exit valves, which escapes at the pipe P.