A PASSENGER.
As the captain positively states that the safety valve was open, he must be believed: the doubt expressed by " a passenger," as to the fact, except until about three minutes of the explosion. may be explained by the facts discovered by Mr Perkins, viz: 1. That " steam highly surcharged with heat, when rushing from the safety valve, or any other aperture, may be known by its perfect invisibility, even in the coldest clay: it is, however, he says, condensible, as may be seen by holding any cold substance in its range." 2. " The whistling " mentioned is another proof of the highly heated steam in the boiler : for, Mr Perkins found by a truly important experiment, that steam highly heated, when issuing from a small aperture, produced such a noise.t The fatal accident on board the Oliver Elsworth in March 1827, near Saybrook, when on her passage to New York, may be ascribed to the same cause. During a " heavy sea and high wind from the S. NV., the boiler burst by collapsing the main flue, and forcing out the furnace head with a tremendous re port, louder than the heaviest cannon." Mr. E. Ha zard judiciously asks, " supposing the water to have been at its proper height in the boiler, may not the motion of the vessel from a head sea have left portions of the boiler exposed to the fire for a length of time sufficient to make them red hot?" A boiler about eighteen feet long at Kensington, Philadelphia county, in which the water had been greatly, if not entirely expended, owing to the fire being kept up during the absence of the fireman at dinner, collapsed from the over heating of the return flue, which was reduced from one foot in diameter to two inches.
Stoppage of the The L'Ina. This was the second steam-boat in which an explosion took place in the United States. It happened in May 1824, between Washington in New Jersey and New York. The Etna had three boilers below deck, and on the high pressure principle, and all new. The feed pipe of the centre one was longer than the other two, and near its internal extremity was bent; a cir cumstance that favoured the deposition of the solid contents of the brackish water which had been used to supply them for some weeks, and which did not take place during the several years she had previously ran in the Delaware. Hence the supply of water was cut off from this boiler, which is known to have become red hot, and must have been nearly empty. It was ob served too that just before the explosion the pressure was diminished from l I101bs. to 50 lbs., owing no doubt to a sudden projection of a limited portion of the re maining water into the hot vapour, of which the heat of temperature became latent heat, and in this condi tion was less efficacious in producing pressure than it had been in the free state.
It was ascertained that at the time of the explosion, the engine was making only eighteen strokes per minute, and had often made twenty-two; the common rate of working was twenty strokes. The first joint of the boiler over the fire was torn off, and driven up through the wheel-house, not in the direction of the boiler, but at a considerable angle, breaking the arms of the wheel; the body split in a spiral form, one and a half turns, and was thrown up flat on the deck, with the exception of the back end, which retained its form from the strength derived from the cast iron bead.
The explanation of the mode in which the explo sions take place from the loss of water is as follows: In consequence of the continued application of fire, or of highly heated steam to the upper part of a boiler, when not covered with water, it becomes red hot,* the cohesive power of the metal is greatly weakened, or destroyed, technically "nealed," and may be easily broken with a slight force. A boiler thus weakened would be unable to resist the pressure of the highly heated and expansive steam produced from the continued fire under the above circumstances, and might burst before it was subjected to a pressure sufficient to raise the safety valve. This effect is more certainly produced by water coming in contact with the metal when in this heated state, an event which Mr. Perkins suggests may take place " by the weight being taken from the safety valve, or by a small rent occurring in the boiler owing to the pres sure of the steam, when an explosion will be sure to follow." The water would also be forced up by the opening of the throttle or safety valve, as has already been mentioned; and in any of these cases, the water being relieved from the pressure of the steam on its surface, would rise with it in proportion to the rapidity and suddenness of its escape. Such instances have been noted above. Mr. Perkins states, that in the case of the English boat Graham, twenty pounds had been taken off the safety valve just before the explosion took place. Two explo sions in cotton mills in France, which are quoted by Arago, and said by him "to appear so para doxical as to excite a doubt," may be added to the above cases. While the steam engines were work ing very slowly, the safety valves opened, and the boilers burst ; no doubt the water in both cases had descended too low, and the upper part of the metal had become red hot. In respect to one, it is stated that the workmen " supposed it to be almost void of steam." Another similar case occurred in a low pressure engine at Lyons, and is noticed by Arago. In all these, the steam must have received an excess of heat, without acquiring a proportionate elasticity : hence the engines worked more slowly than usual, but when the water rushed up, on the overheated metal, highly elastic steam was formed, and the mischief produced. The same effect may ensue from the at tempt to remedy the neglect to supply the heated boilers with water, by pumping in cold water, until it rise to the level of the overheated and weakened part of the boiler. To this cause may have been owing the fatal explosion that took place on board the steam-boat Tricolor at Wheeling, on the 19th April 1831. A letter states " that she had been puffing off steam in the morning, until 9 o'clock, and that the explosion happened the instant the engine was start ed, and cold water was injected into the boiler." Upon examining ruptures in boilers, they have some times been found to follow the water line.