Mr. WILLIAM CHAPMAN, of Newcastle-upon-Tyne, Civil Engineer, examined. Considered all engines, whether high-pressure or low-pressure, as dangerous to the passengers, unless due precaution was taken to emit the steam, when exceeding a given pressure; for, in low-pressure engines, the boilers were always liable to burst, or to alter their force, when the pressure became greater than the resistance, All wrought-iron boilers, but those that were cylindrical in the section, and with hemispherical ends, or portions of spheres, or cones, or coniads, were liable to alter the form by the natural expansive force of the steam, and therefore all boilers of those forms owed their safety to their weakness, because, if weak, they would alter their form without danger, and, if strong, they have been known to bend the iron so abruptly as to break asunder. There were high-pressure engines, working with a force of from fifty to sixty-five pounds per inch, and no accident had happened to any of them but to one, the safety-valve of which was stopped up by a man sitting upon it purposely. He said, he would have a good start, and surprise them. The consequence was, the boiler blew up, and killed and wounded a very considerable number of people.-Considered that the high-pressure engine could only be rendered safe by having the boiler of the form already described, and the cylindrical part of an unlimited diameter, with a competent thickness of wrought iron or copper, and the plates secured to each other by a double line of rivets. It was also requisite that there should be two safety-valves, each laden with any determinate weight per superficial inch of the narrowest part of the seat of the valve. One of those valves should be at perfect liberty to be raised at the pleasure of the manager, because sometimes it was expedient to raise it. The other should be under a cover of such description as not to be opened at all at the discretion of the engineer, but with sufficient apertures for the emission of the steam, and for any of the passengers to see that the valve was not made fast. It was also requisite that there should be a mercurial gauge of not less than an inch in diameter, and whose longest limb should not be greater than two inches and one-eighth for every pound per inch upon the safety-valve for each. It was necessary, by occasional inspection, to take care that the mercury did not stiffen by oxydation, occasioned by the heat and motion to which it was in a slight degree liable.-Conceived that a high-pressure engine, thus guarded, might be used with perfect safety on board a steam-boat, so long as the boiler was kept in order; but the boiler bottom was liable to erode or consume by the action of the fire, and therefore required watching.-Thought a boiler might last twelve months, provided its bottom was made of charcoal-iron, beat, not rolled, because there Mr. WILLIAM CHAPMAN, of Newcastle-upon-Tyne, Civil Engineer, examined. Considered all engines, whether high-pressure or low-pressure, as dangerous to the passengers, unless due precaution was taken to emit the steam, when exceeding a given pressure; for, in low-pressure engines, the boilers were always liable to burst, or to alter their force, when the pressure became greater than the resistance. All wrought-iron boilers, but those that were cylindrical in the section, and with hemispherical ends, or portions of spheres, or cones, or coniads, were liable to alter the form by the natural expansive force of the steam, and therefore all boilers of those forms owed their safety to their weakness, because, if weak, they would alter their form without danger, and, if strong, they have been known to bend the iron so abruptly as to break asunder.- There were high-pressure engines, working with a force of from fifty to sixty-five pounds per inch, and no accident had happened to any of them but to one, the safety-valve of which was stopped up by a man sitting upon it purposely. He said, he would have a good start, and surprise them. The consequence was, the boiler blew up, and killed and wounded a very considerable number of people.-Considered that the high-pressure engine could only be rendered safe by having the boiler of the form already described, and the cylindrical part of an unlimited together, and secured by strong wrought-iron bolts. From observing the danger arising from the introduction of flat cast-iron ends, had invariably terminated the ends of the boilers by wrought-iron ones, nearly hemispherical: this mode of construction, so far as his experience had gone, combined more strength and durability than any other. The precautions he had used to guard against the nuisance of such boilers, had been by adapting to them two safety-valves; one under the control of the engine-man, the other secured in a strong cast-iron case, locked down, and loaded with such a weight, as would suffer the steam to escape when it had arrived at an improper degree of expansive force; safetyvalves not having at all times answered the purpose intended. Had, likewise, in every instance, attached to the boiler a mercurial column, the bore of which was proportioned to the size of the boiler; and considered an iron tube, of an inch diameter, sufficient to guard against accident, when applied to a boiler four feet in diameter and twenty feet in height; because the limit given by such a column came far within the limit of absolute safety. The external limb of the mercurial gauge had, in all cases, been proportioned to the strength of the boiler applied, taking care that the expansive force of the steam would displace the mercury long before any dangerous expansive force would arise. In order to guard against the boiler being injured by the was a great deal of difference in the grain.Would recommend all the boilers on board steamboats to be made either of copper, or charcoaliron plates, beat under the hammer, and not rolled. The resistance of the cylindrical boilers would be precisely in the inverse ratio of the diameter. Mr. PHILIP TAYLOR, of Bromley, Middlesex, Manufacturing Chemist, examined. Considered the first and most material point to attend to in the construction of high-pressure boilers was, that their diameters should be small in proportion to their capacity; that as small a proportion of the external surface of the boiler as possible should be exposed to the destructive action of the fire; and that that portion of the boiler which was subjected to the action of the fire should be so situate and guarded, that, in case of explosion, the least possible mischief should arise. In all boilers which he had made use of, no portion of the boiler was exposed to the action of the fire, without its being constantly covered with water. In the boilers constructed. under his direction, the fire was applied under an arch of not more than two feet and a half in diameter: this provided against any extensive rents taking place in the event of explosion. All the boilers he had hitherto employed had been constructed of malleable iron, commonly known by the name of charcoal-iron, rivetted |