Page:Report from the Select Committee on Steam Carriages.pdf/146



Mr. Richard Trevithick. 17 August, 1831. exploded, and this generally takes place immediately on setting the Engine to work; when the boiler is under water guage it must be red hot, and while the Engine is standing the water in the boiler is still, but the moment that the Engine starts, the sudden escape of steam from the boiler to the cylinder causes a great ebullition of the water, and splashes it over the red hot sides, which instantaneously generates a superabundant quantity of steam more than the strength of any boiler, however strong, can sustain, because one pound of melting iron will boil three pounds of water, therefore the red hot tubes of a boiler to be suddenly cooled by water splashing over them, would immediately generate a hundred times as much steam as the space of the boiler would contain, therefore while the feed is so uncertain and the height of water fluctuates so much in the boiler, no permanent safety can be relied on, however light the safety valve may be loaded, or strong the boiler may be; boilers fed with salt or even foul water are dangerous, they are often incrusted with salt, repeatedly heated red hot and quickly reduced in substance and strength. To prevent the salt accumulating, a constant stream of boiling water is ejected from, and cold water in its stead injected into the boiler, which occasions a constant fluctuation in the height of water in the boiler, and requires a constant caution in the Engineer to prevent mischief. A proof that boilers do not explode from the regular working pressure of steam, is by the portable gasholders of one sixteenth of an inch thick and ten inches diameter being regularly charged with thirty atmospheres, or 450 pounds to the inch without accident, and though this pressure is not one-half the pressure that the theory of the strength of iron would bear, yet boilers have often exploded, though the safety valves have never been loaded with one-eighth part of the pressure of the gasholders, or one sixteenth of the pressure of the theory of the strength of iron in proportion to the strength and diameter of boilers, when compared with the gasholders; therefore perfect safety can never be relied on under the present regulations. To remove these serious evils,