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the engines (used in steam boats) hitherto used in Scotland have been made on Mr. Watt's principle; but those in America have been high pressure engines; which being more simple and less expensive in the first instance that is some of them have been constructed in England: but one of them having exploded in an American boat, the proprietors of some of the English boats have changed their engines for others on Mr. Watt's principle, to avoid similar accidents. We think it quite unjustifiable in any engineer, to advise the construction of steam boats with high pressure engines; at least for passage boats; in which so many persons are always assembled together, and so near to the engine, that they would all be destroyed in the event of a boiler bursting.'
Since that was written, very serious accidents have happened on board the Norwich packet in England, on board the Enterprize at Charleston, and the Oliver Evans steam boat on the Mississippi in this country. It is not merely from the boiler bursting that danger arises where a high pressure engine is used; for in the case of the Norwich packet, the steam swept away the boiler itself, and this swept away every thing and every person that stood in its way at the time of the explosion; and was thrown in a horizontal direction out at the stern of the boat. Phil. Mag. Ap. 1817, page 300.
Fulton never would use any engine of this description, and in a conversation with the writer of this article, he promised to send him the model of a machine that should prove beyond doubt that at the same expense of fuel, there was not only more safety but more power in the condensing engines. Certain it is, that the accidents on board Fulton's boats by which life or limb were lost or even jeopardized, have not been recorded, nor have we heard of a single accident arising from Boulton and Watt's engines in England, during forty-five years practice throughout the kingdom.
The advantages of high-pressure engines are
1. They are more simple in their construction: the condensing box, the injection pipe, the well, the well-pump, and some other parts of Watt's engine, are dispensed with.
2. For the same reason they are cheaper in the first cost.
3. The cylinder is smaller, and the whole machine occupies less space than an engine of the same power on Boulton and Watt's construction.
4. The power may be more easily increased, on an emergency, than in the condensing engine.
As to the permanent expense in fuel, we believe the advantage on fair experiment will be found in favour of the condensing engine; which, under circumstances equally favourable, will afford more power with the same expense. Indeed, so much water is converted into high steam, and thrown away in the open air in one of Trevethick's engines, that this conclusion is very probable a priori. Boulton and Watt have never chosen to erect one on this construction, among a thousand that have been built at their works. We know of no other advantage that can be stated in favour of employing high pressure engines. On the other hand,
1. The condensing engines are safer: Fulton's boats can be driven above five miles an hour, with steam that does not press more than six pounds on the square inch; and where are the accounts of lives lost on board his boats by explosions, during the ten years they have run, fourteen now running in New-York state? A high pressure engine working with one-hundred and fifty pounds of pressure on the square inch, presses with a force equal to twentyone thousand six hundred pounds on the square foot of one hundred and forty-four square inches: while a condensing engine, working with six pounds on the square inch, presses only with eight hundred and sixty-four pounds on each square foot withinside the boiler. Hence it is manifest at once, to every man, whether he be an engineer or not, (a) that a boiler cannot be so much forced by a pressure of less than one thousand as by a pressure of more than twenty thousand pounds on the square foot; (b) that if an explosion takes place by over-loading a condensing engine, it will only make a rent in the boiler, and the steam will escape; for as a boiler which is to sustain only a thousand pounds weight of pressure on the square foot, need be only the twentieth part as strong as one that must sustain a weight or pressure of twenty thousand pounds op the square foot, steam much weaker, more condensible, and less dangerous, will burst the one boiler, than the other: (c) Hence in case an explosion should happen, the steam will be comparatively harmless in a condensing, compared to the steam of a high pressure engine: the former will scald nobody at six feet distance; the latter will scald every man on board the boat; the former will only make a rent in the boiler, and escape and be condensed, the latter (as in the Norwich packet) may carry away the boileritself even where it is too strong to burst. It may be granted that the diameter of a cylindrical boiler may be so diminished as to annihilate the hazard of burstinga thermometer tube may resist any pressure that even a steam engine can give withinside of it; but there is a point in practice beyond which the length of the boiler cannot be extended and the caliber cannot be diminished. So that, we must reason from what practice and experience will permit or compel us to use. Mr. Oliver Evans, whose patent is two years later than Trevethick's, and whose form of boiler was for some years exactly the same as Trevethick's, viz. a long cylinder with a flue passing through the centre of it, the ends secured by cast iron flanches-has judiciously altered his original plan, by rejecting the internal cylindrical fireplace, a source of much danger when the water is by any accident permitted to be too low withinside, and by substituting strong sheet-iron for cast-iron, except we believe as to the door that closes the ends. In fact no part of the steam engine exposed to the pressure of the steam ought to be of cast iron at all. These are improvements: still, should an accident happen, steam at the temperature which one-hundred and fifty or two hundred pounds on the square inch indicates, is full as bad as gunpowder; it is not speedily condensible by the common temperature of the atmosphere, and
therefore it is calculated to force away all before it, in every direction; to scald by its heat, and to rend by its force.
2. The advocates of condensing engines ask, that while machines of this description are so much safer in comparison than the others while they are competent to propel a boat against wind and tide nearly six miles an hour, why run so much risk for such little ad. vantage?
3. They say further that in the long run, the condensing engines are not only safer, but cheaper: they consume somewhat less fuel in performing the same service, and they last longer in consequence of not being so much strained, and racked, as a high pressure engine is, and from its construction must be. The packing of one of Watt's engines will require to be renewed once a fortnight perhaps; an engine of one-hundred and fifty pounds on the square inch of the safety valve, once every two or three days. Near this city, an experiment can easily be tried which would settle the question in practice here. At the new water works near the upper bridge over Schuylkill, there are two engines, one of Oliver Evans's construction working with steam that presses one-hundred and fifty pounds on the square inch, and a condensing engine that works with four pounds on the square inch; both built to be of the same power, and to be applied to the same work. Some slight alteration however will be previously necessary:
Let the fire place of the condensing engine be somewhat enlarged, and the mouth of the fire place turned (like that of Mr. Evans's engine) toward the water, so' that each shall have the same advantage of a current of air; for in their present state, no certainty would be the result of the experiment. These alterations being made (which in fact must be made) then see which engine performs the most work with the same quantity of fuel in twentyfour hours. For this is the true question, what is the daily expense of fuel? The original expense of an engine is comparatively nothing; and indeed the actual difference in the expense of the two kinds of engines is little: the great expense of an engine is the fuel it consumes.
At what value in fuel can each of these engines do the work of a horse; that is, raise thirty-two thousand pounds weight, one foot high per minute?
The condensing engines of Boulton and Watt in Cornwall in the first four months of the year 1816 raised about twenty-eight and a-half millions of pounds of water one foot high for each bushel of coals consumed; the coals weighing eighty-eight pounds per bushel, which is the regular London weight of a bushel of coals.
Woolfe's improved double engines, raised upwards of fifty millions of pounds weight one foot high, for the expenditure of each bushel of coals consumed.
We do not say that this great effect will be produced by every engine of Watt or Woolfe. Watt's engines at first raised only thirteen and a half millions of pounds weight for the expenditure of one bushel of coals, but when the steam engine owners of Corn
wall combined to pay Messrs. Thomas and John Lean- for taking a monthly account of the actual work done by every engine at every mine once a month, the engineers gradually improved in the care they took to keep every part of the engine in good order, until from thirteen and a half they raised the average work to twentyeight and a half million of pounds avordupois, raised one foot high, by means of eighty-eight pounds weight of fuel.
Boulton and Watt contract that their engines shall raise five hundred thousand cubic feet of water one foot high at the expense of one hundred and twelve pounds weight of coal. Every cubic foot of water weighs sixty-two and a half pounds avordupois: this will be, more than twenty-four millions of pounds avordupois raised one foot high, by means of one bushel of coals weighing eightyeight pounds.
It seems however that in practice the large engines do more work for the same fuel than the small ones.
It will easily be conceived how much more important the consideration of fuel is than the mere first cost of the engine. Suppose for instance, one of the engines at the Schuylkill works, moved at its regular rate for three hundred days in the year, morning and night, and consumed daily eight cords of wood, at seven dollars per cord on the average laid down at the works—the annual expense of fuel alone, would be near seventeen thousand dollars a year!
4. The advocates of condensing engines say that they admit of more precautionary measures of safety than the high-pressure engines. (a) The boiler may be made of sheet iron that will rend instead of bursting: or (b) with equal convenience of copper, a material commonly used in England: (c) the proportion of water and steam can be more easily indicated in the boiler of a condensing engine than in one of high pressure. (d) The self-acting damper that stops the draught when the steam by negligence or accident is raised too high, is an effectual security which cannot be easily adapted to a high pressure engine: (e) when the steam is too high it can esi cape by blowing through the tube that supplies the boiler with hot water in a condensing engine.
Such are the chief arguments on both sides of this question, which is now anxiously occupying the public in England generally, and a parliamentary committee in particular, whose report we may expect in a few weeks.
The following precautions have been suggested in England:
To try the strength of the boiler by the injection of water under a pressure. This has also been recommended by judge Cooper, Mr. Perkins, Mr. Cloud, and Mr. Graaf, to whom a committee of the common council of Philadelphia applied for their opinions.
To have double safety valves to every engine. Mr. Woolfe, who Qever works higher than forty pounds, and lets off his steam into a second cylinder, uniformly attaches a second safety valve to his engines. This was recommended by the above named gentlemen, and previously also by Mr. Hare in this magazine.
• To have a mercurial guage, pressing on the safety valve with a column of mercury, which in case of the steam being too much raised will blow out. Our objection is, the aperture will be too small to answer the purpose
of safety To have a plug of fusible metal in the boiler: this was Mr. Trevethick's plan, and absolutely necessary to such boilers as have the fire inside the water cylinder: but it has been seldom adopted by other builders of high pressure engines.
To strengthen the partitions between the engine and the passengers, and to weaken the other parts of the enclosure; so that when the steam exploded, it should issue out at the place of least resistance, and the furthest from the passengers. This was the suggestion of judge Cooper, and Messrs. Cloud, Perkins, and Graaf, in imitation of the practice at gunpowder manufactories; and indeed seems to be one of the most valuable measures of precaution hitherto recommended.
Lastly, to prohibit by legislative interference, the navigating of passage boats by means of high pressure engines, as being dangerous, unnecessary, and calculated to give alarm even when the danger is slight.
This measure is objected to, because, the legislature ought not to interfere in the management of a man's private business-because this legislative interference will arrest the progress of improvement in machinery--because every man is the best judge of the risk he chooses to run-because this measure would give
indirect and unfair advantages to a particular kind of manufacturebecause boilers can be made to resist any force whatever that can be applied to them
because this kind of interference would be equally vexatious and unnecessary. To these arguments it is replied:
That the legislature is not requested to interfere in private but in public business. The application relates to steam passage boats alone. Owners of manufactories are at liberty to erect whatever engine they choose, and to run whatever risk they choose. But carriers and passengers have at all times, in all civilized countries, been objects of legislative care and controul. The legislature is called on to prevent the wanton destruction of lives by persons who are careless of every thing but their own emolument. A passage boat is as much an object of regulation as a stage coach; and wilful, needless risk of danger, and danger arising from culpable negligence are equally objects of regulation and of punishment in the one kind of vehicle, as in the other.
That such an interference will not stop the progress of improvement, while every private manufacturer is at liberty to erect whatever kind of steam engine he pleases, at the risk
his own person and his own property. Whenever, by a long course of experience in manufactories, the high-pressure engine shall be found perfectly harmless, let the act interfering with them be repealed. In mean time, the present division of opinion among scientific men, is of itself a sufficient reason for the legislative interference. If an engine