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To the Editors of the American Railroad Journal and Mechanics' Magazine. GENTLEMEN-I was somewhat surprised, to find in your number published on the 15th inst, a paper signed "An Engineer," the writer of which appears to have been highly offended at the liberty taken by myself with Professor Renwick's account of the steamboats of the United States; and he takes the opportunity to read me a very edifying homily upon "a proper spirit, and facts sufficiently strong." These are undoubtedly necessary in properly discussing any subject, and where one of the parties engaged is nearly, or quite destitute of both, the other must supply the deficiency, if any good results from the discussion. To this paper I feel bound to make some reply: but as I have no other object, in doing so, than to place the matters in question in their true light, I shall avoid any remarks not having a direct bearing upon them. I am bound, first of all, however, to plead guilty to the "Engineer's" charge of delay.
But, as he appears quite displeased with my remarks, now they have ap peared, I am somewhat surprised that I am charged with criminal neglect, in not sending them forth at an earlier day. In extenuation of the fault, I beg leave to say, that I am not so fortunate as to obtain every English work immediately on its publication, and also, that at the time of receiving this, (which was several months since,) a serious accident, rendered me unable, even to read, much less write comments upon any portion of it. The next thing which "an Engineer" complains of, is the table showing the consumption of fuel by different engines, and says, "the things in this table which are stated as facts, are not only contradicted by every valuable work on the steam engine and by practical experiment, but by the authority of the English, and by the words of the great perfector of the engine, Watt." He then proceeds to show that I know nothing of the English method of calculating the power of a steam engine, and prove it, by refering to "page 146 of Stephenson's Civil Engineering in North America." The figures which are quoted, are certainly set down in the book, but if "an Engineer" has not forgotten all his arithmetic, and will read the calculation over again, he will see that 748 is a typographical error; and all that is said of the Great Western, by Stephenson, is that her engines are said to be 450 horse power." Will "an Engineer" please to make use of the formula which he will find at the same page, and calculate for himself, the power of the Great Western. The result will vary very widely from 450. And here I beg leave to refer the writer to one English work of some value, in which he will find a part of the details of an experiment, and some opinions which do not exactly contradict my own. In "Tredgold on the steam engine and steam navigation," page 365, vol. I, in an account of the steam packet Ruby," it is said, "the safety valves are arranged upon the plan invented and used by Messrs. Boulton and Watt, a long time since, and now generally adopted by the Engineers of London. They are so arranged that no one on board can possibly have access to them; the engine man can at pleasure open thein and let the steam escape, but he has no
means by which he can keep them down, beyond the weight placed upon them by the engine maker, which weight is, as before stated 31⁄2 pounds on the inch; and it is a curious fact, that this boat has attained the great speed named, with this small pressure, while in a variety of instances vessels from different out ports, working with high pressure steam, and with the safety valves loaded ad libitum, by the engineers and captains, have never been able to approach her in speed. This clearly proves, what Mr. Watt demonstrated long ago, that the most efficient, safe and economical mode of working steam engines for marine purposes, is at the pressure of from 21 to 3 lbs. on the inch. At the same time, for single acting pumping engines, there is no doubt an advantage gained by the judicious use of high pressure steam, say of 30 lbs, on the inch working expansively, with boilers properly constructed, but which boilers, for many reasons are not at all fit for steam vessels; in fact, almost all the melancholy accidents that have occurred to steamboats by the explosion of their boilers, have been caused by the injudicious application of high pressure boilers to marine purposes." And on the next page, it is said "the high pressure steam system, has been the means of filling the journals with those ever-occurring, heartrending, and sickening details of hundreds and thousands that are being yearly sacrificed to ignorance and prejudice, by attempting to do that by the dangerous use of high pressure steam, which can be so well effected by steam of a low pressure, and that too at one half the consumption of fuel." The practical experiments which contradict the facts set down in the table "an Engineer" has not given us, and should he attempt to find them, he would be obliged to report non est inventus. The table is merely a statement in a convenient form, of such information as I was able to obtain by careful inquiry, and it may possibly contain some errors-my personal knowledge could not, of course, extend to all the cases and I was consequently compelled to rely upon the accounts received from others, or contained in printed documents. And if "an Engineer" possesses more correct information, and will show in what particulars it is incorrect, I shall with much pleasure make the necessary corrections, but until errors are pointed out, I shall suppose my information was of the right kind, obtained from the proper sources, and the table correct. But "an Engineer" might have said, with truth, that the table is now incorrect, although it was correct at the time it was compiled. The Rochester then had a 43 inch cylinder, which has since been exchanged for one of 50 inches diameter, (the boiler and other parts of the engine remaining the same.)
The result of this change is, that the steam, furnished by the boilers, is worked a lower pressure upon a larger piston, and the power of the engine increased at the same time and by the same means that the danger of explosion is diminished. That the pumping engines in Cornwall use steam of 40 lbs. pressure per inch, and work it expansively, I very well know, but I know also, that all attempts to use the same plan and pressure in double acting engines, employed in any other
kind of work have hitherto failed entirely to effect the same saving in fuel as is said to result from its use in pumping. The gentleman will find abundant proot of this in vols. I and II of the "Transactions of the Civil Engineers," the study of which, I beg leave to recommend to him, for he appears to have read the work carelessly or hastily, or he would never have referred to page 127 vol. I, for proof of Mr. Watts' partiality to high pres. sure steam. At that place is an extract from his specification filed on taking out the patent for his expansion engine. The steam mentioned there of 14 lbs. per inch, is that which would be measured by the common steam gauge with the index at zero-that is, steam just counterbalancing the pressure of the atmosphere.
The advantage of working expansively is admitted, and has never, so far as I am informed, been denied or hardly questioned, it is safe and economical; but as I have before remarked, all its advantages may be obtained without venturing even into the neighborhood of Professor Renwick's cheap and moderate pressure of 57 lbs, per square inch.
The Engineer's" quotations from Redfield deserve a passing notice too, because, as they stand, the conclusion must be inferred from the premises, and it ought to be stated. And in order to have the clearest view of the matter we will put it in the form of a syllogism, which will stand thus. Steam of 7 lbs. pressure per square inch, is dangerous.
Steam of 18 lbs. pressure per square inch, is less dangerous.
Therefore, as the pressure is increased the danger is diminished. This being the legitimate conclusion, the question very naturally arises, how high must the pressure be to have the danger disappear entirely from the calculation, or if it retains its place, will it not appear with a negative sign if the pressure is sufficiently high? This question is a curious and interesting one, and I shall be pleased to have it answered by "an Engineer." Meantime, I remain
Novelty Works, May 20, 1840.
Your obedient servant,
JOHN D. WARD.
MEMOIRS OF THE MOST EMINENT AMERICAN MECHANICS ALSO LIVES OF DISTINGUISHED EUROPEAN MECHANICS, TOGETHER WITH A COLLECTION OF ANECDOTES, DESCRIPTIONS, &c. &c. RELATING TO THE MECHANIC ARTS-ILLUSTRATED BY FIFTY ENGRAVINGS BY HENRY HOWE.
We have had the above named work for some time before us, but have not until now had an opportunity of noticing it. Mr. Howe has aimed at making an instructive and readable book for mechanics and others interested in such memoirs-aad in fact who is not interested in the narrative of the struggles, experiments, partial failures and final success of men who have, in some instances, conferred inestimable benefits upon mankind.
In the work before us it will be found, that there are lives of Fitch, Evans, Slater, Whitney, Bushnell, Whittemore, Blanchard, and Eckford,