When the Etna ran in the Delaware, with a high pressure engine, a leak in the bottom of the boiler took place, owing to the collection of sediment in it, but no injury was sustained by any one: and the burst ing of one of the boilers of the Bristol, already men tioned, proceeded from the same cause, according to the opinion of the captain. '' The small space between the bottom of the furnace and the outside shell, was very difficult to be kept clean, and that was the spot where the rent took place." This was doubtless heat ed red from the accumulation of coals underneath the bars of the grate. ' The boats plying in the muddy and sandy waters of the western country, are particu larly subject to danger from the accumulation of sedi ment.
10. The Sudden Increase of the Pressure of Steam on a Boiler.
A sudden increase of pressure of the steam 'on a boiler, there can be no doubt, has often occasioned explosions which could not be accounted for by any apparent defect in it, owing to the unequal expansion of the metal which ensues, on the same principle that hot water poured into a glass or china cup will cause it to crack. The bursting of the boiler in the tobacco manufactory at Chester in England, already referred to, took place from this cause. Mr. Leet relates that " it was connected with machinery requiring steam of great expansive force for its movements, and when used for the first time since its repair, the steam was speedily raised in such a powerful manner, that the boiler was perceived to have an oscillating motion for a considerable time, and finally exploded, spread ing desolation all around." A greater pressure, if produced gradually, might not have been attended with any rupture.
It has been mentioned that owing to the explosion of the Etna, a prejudice arose against high-pressure engines for steam-boats, and that those in the Atlantic waters have since that time been supplied with others on the low-pressure principle. The term low-pres sure is, however, most commonly, merely nominal; for there are few boats professedly working with low steam, that do not carry many more pounds to the inch than the low-pressure principle, or the strength of their boilers will warrant. On the western waters this is notoriously the case. From a well-in formed and highly respectable source, it can be stated, that "many boats in those rivers run under the name 'low-pressure,' merely from the circumstance of their having the condensing apparatus, and from disposing of the steam by that means as distinguished from those which suffer it to escape in the air, al though it sometimes happens that the condensing boat uses steam of a greater density than the other, called high steam.' Boats thus working the high steam,
but condensing, are technically termed medium engines.' It was formerly thought that a good va cuum could not be maintained in the condenser when working high steam, but practice as well as theory teach otherwise, for from the same boilers and fuel burnt, an equal quantity of heat passes to, and has to be overcome by the condensing apparatus, whether the steam operate through a small cylinder under high pressure, or through a large cylinder at a consequent low-pressure. It is not unrrequent for boats on the Ohio and Mississippi, which condense their steam, to work it as high as eighty to one hun dred pounds per square inch; now the nett gain by condensing is not in any engine much over ten pounds to the inch, so that this little apparent increase of force is scarcely worth the expense and care of condensing;" and besides, it is lost by the reduction of temperature, which must be below one hundred and seventy degrees; whereas when supplied from a high pressure engine, the water would be two hundred and twelve degrees; but the steam is disposed of in an in sensible manner, and the boat obtains the security creating name of " Low Pressure:" how justly, let the above remarks determine.
It has already been stated, that notwithstanding the prejudices in the public mind against high pressure engines on board of boats, those propelled by low pressure, were as much liable to explosion as others driven by high steam. The following list comprises the cases of some of the accidents, which have oc curred in low pressure boats.
1. Paragon of New York, built by Mr. Fulton.
2. Atalanta, running between New York and Eliza beth Town.
3. Washington, on the Ohio, June 1816.
4. Powhatan, between Norfolk and Richmond, March 1817.
5. Bellona, New York and New Brunswick, March 1822.
6. Eagle,* Baltimore and Annapolis, April 8,1824.
7. Maid of Orleans.
8. Cotton Plant of Mobile.
9. Superior, of Charleston, South Carolina.
10. The Rariton, of New York.
11. Oliver Elsworth, March 1827, near Saybrook, Connecticut.
12. Constitution, 1825, North River.
13. Legislator, 14. Carolina, Waters of New York.
15. Franklin, 16. Chief Justice Marshall, off Newburgh, North River, New York, April 22, 1830.
17. United States, Sept. 11, 1830, in the East River, New York.
18. Tricolor, at Wheeling, on the Ohio, April 19, 1831.
In all of the above cases, more or less persons were killed outright, or died soon after being scalded, tor were disfigured or crippled for life. The greatest number suffered on board the Helen NFGregor. Fifteen hun dred persons, it has been computed, have lost their lives by explosions of steam engines in Jimerican boats.