In theUnited States steam boats, the fire is made un der the boiler, which returns through flues passing through the boiler, and are connected with the chimney proceeding from it.t These flues, although always in tended to be covered with water, often get uncovered from the causes before mentioned, and become red hot; the metal is expanded, and consequently has its cohe sive power greatly diminished; and this being repeated may give rise to explosions at a time of apparently perfect safety. With careful firemen or captains there may be no danger of the water falling below these flues; but we know that the most wanton inattention has prevailed on board of steam-boats to this important point. It is therefore necessary to diminish the sources of danger to travellers, by placing them as much as possible out of the power of ignorant, ob stinate, or negligent men. The four cases of col lapses in Cornwall, referred to by Mr. Taylor,t occur red in boilers with return flues. The Chief Justice Marshall and United States, in the waters of New York, also had them; and several others that have exploded.g They are indeed commonly introduced at present.
The Constitution (first named the Oliver Evans,) which was the first boat that exploded on the Ohio, was built with flues passing through each boiler, by Mr. Geo. Evans, who deviated from the plan adopted by his father. Having proved them with" a pressure of 200 pounds to the square inch, and regulated the safety valve to pounds, he thought them perfectly safe, but more might have been employed; if not, no other cause can be assigned than neglect to keep the water above the flues. He concludes by saying, " flues of this description are not safe, and ought not to be used." On the western waters of the United States, flues are not only generally introduced into high pressure boilers, but under circumstances peculiarly dangerous. In a boiler of thirty inches diameter, the flues are from ten to sixteen inches in diameter, which often leave no more than a space of fuur inches between the bottom of the boiler and the lower flue, and ft (An ten to sixteen inches for water and steam room; and hence from in attention on 'the part of the fireman, the water may soon fall below the flues, and by becoming red hot they are rendered liable to explosion. The flue of a boiler at Kensington, Philadelphia county, which col lapsed, -vas sixteen inches diameter, and the two sides came close in contact. In the boiler at the distillery called Lochrin, near Edinburgh, and at the tobacco manufactory at Chester in England, the bottoms of the boilers, which were convex to the interior on the side next the fire, to allow the flame from the furnace to play in the centre almost of the liquid, were ren dered convex outwards, so strong had been the pres sure from within.
Mr. Taylor states that at East Crennis Mine, Corn wall, the inner tube was compressed as if the fire had softened the part above it, though there did not appear to be any other reason to think that the water was too low. At the Mold mines in Flintshire, the inner tube was not moved from its place, although it was very much flattened for a great part of its length, the sides having come together.
A writer under the signature " An Engineer," in commenting upon the cases of explosions in Corn wall, related by Mr. John Taylor, says he " con
siders the introduction of a tube within a high-pres sure boiler to be bad under any circumstances, but it is particularly so where the furnace is placed in it. The ash-pit, also, is by necessity most objectionably small, where the furnace is inside the boiler. This is an evil of some magnitude, both as regards the draught, as well as the wear and tear of fire-bars."1 5. Material Composing Boilers.
Boilers were frequently made of cast iron when steam boats first began to run,and gave rise to many explosions, owing to internal defects of the iron, and to its liability to crack from heat. Wrought iron is therefore now generally substituted. It is also preferred to copper, from its greater tenacity. But when salt water is used, copper is preferable, because it acts less powerfully upon the deposits from it than iron. Cast iron even for the ends of boilers is objected to by O. Evans, un less the fire be kept from them, owing to their liability to crack when heated.
6. Use of metals of different expansive powers for boilers.
To this cause may in part be attributed the explo sion of the Norwich Steam-packet. Ic was ascertained that the boiler, although cylindrical, had one end of cast iron, the other of wrought iron. These ends were flat. The cast iron end was only of an inch thick, and it was this end that gave way. The body of the boiler was composed of wrought iron. The propriety of only using one kind of metal for a boiler must be obvious.
7. Weakness of the boilers from long use; unequal thickness in the metal; and raising steam too high for its strength.
The influence of these causes is apparent to all. A boiler sent to Mr. Oliver Evans to repair, had been reduced to the thinness of paper in se venal places, and had been used in this dangerous state for some time. It had discharged its steam in two or three instances, through a small vent, without however injuring any one. A boiler of the low pres sure steam-boat Bristol collapsed, from this cause, in the spring of 1820, in the Delaware. There were two boilers, one on each side of the engine, connected with steam and water pipes. The top of the furnace was flat. The boilers were old and corroded, and the cap tain, who is still living, says that " they ought to have been condemned before he took charge of the boat. There was a great competition from four boats at the time, and the Bristol being ahead of a better sailing boat, belonging to another line, the engineer desired the fireman to increase her fire to preserve her dis tance. The fireman replied that there was as much fire as was necessary, and if he wanted more he might make it himself. He did so, and suffered for his folly. While the captain was in the lire-room, he was alarmed by the leaking of the boiler, followed speedily by a tremendous hissing of steam, and retreated in time. On inspection, it was found that the furnace or {due, in the centre of the boiler, had been forced inward, and the steam and water from both boilers had rushed into the lire of the injured flue, or inside shell of the boiler." The boiler that exploded at the Union Rolling Mill, Pittsburgh, was worn out.