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On their appointment, in 1830, the Committee addressed letters to persons whom they supposed might furnish information in regard to the subject before them, and have published the replies in the same Journal in which their reports first appeared. At the request of the Secretary of the Treasury of the United States, they also undertook two series of experiments; the first intended to test the truth of the various causes which have been assigned for the explosions of steam boilers, and the second to determine the strength of the materials commonly used in their construction. The first-named series of experiments being that upon which the general report of the Committee is based, was published+ next in order to the replies to their letters, and we were thus furnished with the means of judging, independently of the authority of the Committee, of the accuracy of the conclusions in their General Report. The second series of experiments is now in the course of publication.‡

We propose, in the following article, to give as full a view as the nature of our journal will admit of the General Report of this Committee, and of their experiments, inverting for this purpose the "inductive" order, and following the discussion of the causes of explosion as enumerated by the Committee, in their General Report, referring to the experiments as the subjects of them came under discussion.

1st. Explosions may occur from undue pressure within a boiler, the pressure being gradually increased.

It would seem that there could be no difference of opinion as to these being a 66 vera causa." Engineers have, however, alleged that boilers, particularly if made of copper, only rend by a gradually increased pressure, and thus discharge their contents without dangerous violence. A most dangerous maxim is stated, in this Report, to

works are under discussion, are, or were, Professors of Natural Philosophy or of Chemistry. Four other members we find, from the same source, to be practical mechanics. One other has written much on Mechanics. We are thus left in doubt as to the professions of but four, out of seventeen, of the Committee.

Journal of the Franklin Institute, vols. viii., ix., x.

+ Journal of the Franklin Institute, vol. xvii., and London Mechanics' Magazine. The first and second parts of this Report have been printed in a separate form by the Franklin Institute, and kindly presented to several of our scientific societies.

Both series of experiments were made by sub-committees, whose names are given in the Preface to the Report. On neither of them do we find the name of Professor Hare, who is vauntingly said by our cotemporary before noticed, in his attempt to discredit this Report, to have "openly stated that he never attended a single experiment." We do not intend to fatigue our readers by following the disingenuous criticisms of our anonymous friend in detail, considering, as we do, his review to be discreditable to a journal professing to give information upon science. It is the more objectionable because interspersed with general epithets of approbation, which are totally misapplied if the individual criticisms are in the least warranted. Besides perversions of fact, we have, in his review, such language as this:" President Jackson and some of his fellow citizens down east ;"- "There must be a district in Pennsylvania where the shamrock is worn!" &c.

be prevalent among engineers on the western waters of the United States, that, provided a full supply of water is kept in a boiler, there is no danger of explosion from increasing the steam pressure."

To set this question at rest, two cylinders-one of iron and one of copper-were partly filled with water and exposed over a fire, so as to increase the pressure of steam within; the greatest amount of this pressure, before the cylinder gave way, being registered by a spring

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gauge. The material facts attending the bursting of the iron boiler are thus stated by the Committee :-

"The explosion tore off one of the heads, b c, of the cylinder, projecting the other parts of the boiler in an opposite direction, carrying with them, for a portion of the distance, the iron cylinder forming the furnace, and scattering the fuel in every direction. * The boiler head was thrown fifteen feet, the boiler and spring register about six feet, and the furnace, weighing about forty-five pounds, was overturned and carried four feet. The pressure indicated by the register was 114 atmospheres. • * The circumstances

of this experiment show that the steam rose quite gradually on account of leaks in the boiler, increasing, probably, more rapidly as the quantity of water diminished, the intensity of the fire, meanwhile, increasing; that, at a certain period, the tension within had attained about eleven atmospheres, when the boiler exploded violently."

The

copper cylinder was next subjected to experiment:

"As before, nothing remarkable occurred previous to the instant of explosion, and the members of the committee employed in the experiments were engaged in observing the boiler at the instant it exploded. A dense cloud of smoke and flame, capped by steam, rose from the pit; the stones and combustibles were widely scattered, and the boiler was thrown, in a single mass, about fifteen feet from the furnace. The noise attending this explosion was like that from the firing of an eight inch mortar.

The boiler was rent as shown in the accompanying figure, giving way in an irregular line, just above the probable water-line on one side of the boiler, but not conforming to it. d and b were the lowest points in the two heads

This same opinion we see in the evidence of one of the parties examined before the coroner's inquest in relation to the late accident at Hull.

before the explosion. The sheet of copper was torn from the heads, un.

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rolled, and irregularly bent, adhering to the heads for only a short distance near the top of each; and the heads were bent outwards. The thickness of the copper along the line of rupture varies from 0.25 to 0.35 of an inch, and the metal appears to have been highly heated at one end of the torn portion."

To a gradual increase of pressure beyond that which the material of the boiler would bear, the Committee refer certain well-known accidents, which are upon record; as that in Wellclose Square, London, that of the steamer, Rhone, &c.

The safety-valve being the means commonly relied on to prevent a dangerous accumulation of steam within a boiler, the Committee thus enumerate the causes which may render it inoperative :-Design on the part of the engineer or attendant, and adhesion of the valve to its seat by rust or other cause. This adhesion, the Committee consider, cannot be traced to the peculiar phenomenon observed when a disk is placed before an aperture, whence a fluid is rapidly issuing. This phenomenon has been the subject of much examination. The first observation of it is claimed by M. Clement, of Paris, and by Mr. Roberts, of Manchester. Theory and experiment both shew it to depend upon the relative dimensions of the disk and aperture; and as these are not very unequal in the case of the safety-valve, the tendency of the disk towards the opening is inconsiderable. This deduction is further confirmed by the experiments of the Committee, who used a graduated safety-valve, and compared its indications of pressure with those of a mercurial gauge, or with those deduced from the observed temperature of the water in the boiler. Two different valves were used in different parts of the series of experiments, both

being, however, of the same form-disk valves. This form is stated to have been selected as most applicable to practice, from the ease with which the touching surfaces can be ground into contact, and the impossibility of tightening by friction, as in the case of the cone. The observed pressures at which the valve rose were uniformly below the calculated pressures at which, allowing for the weight, leverage, and friction, the valve would have been expected to rise; the mean ratio being as 1 to 1.035. In no case was any undue adhesion observed. While these experiments are favourable to the use of the safety-valve, when well constructed and kept in good order, they cannot be considered as justifying that feeling which imagines a valve to be a security, without inquiring into its condition. On the contrary, we find in this Report a well-authenticated instance of great adhesion of the valve to its seat, requiring, when the pressure of the steam was above that which should have raised the valve, considerable force applied at the end of the lever to open it.

Besides two safety valves, the regulations for the safety of the steam engine, until lately in force in France, required that fusible plates, or plugs, should be placed in or over an opening into the boiler. These, giving way when the steam within reached the melting point of the alloy constituting the plate, allowed the escape of steam. These plates were intended besides to apply to a case in which the safety-valve is inoperative, namely, when, from a deficiency of water in the boiler, parts of the metal have become highly heated, and thus have heated the steam above the temperature corresponding to its density.* The experiments made on these plates were numerous, and lead to a conclusion of considerable interest as affecting their use. It was found that the alloys composing the plates soften, in part, before they reach the temperature of fusion of the whole mass, and that liquid portions are forced out through the holes of the brass plate which, in practice, covers them, leaving a less fusible mass. In the case of one of the alloys, which melted above

The

That steam thus surcharged with heat may exist within a boiler which yet contains some water, appears to have been generally assumed. fact was made the subject of experiment by the Committee, who found it to be as assumed. The steam was produced and kept up by a charcoal fire placed under a boiler, while a similar fire above the boiler surcharged with heat the steam produced. The committee found that the elastic force of the steam calculated on the supposition of its expanding by heat as a gas agreed very nearly with the observed force, differing but .05 of an atmosphere at the temperature of 533°. The thermometer giving the temperature of the water in the boiler had become deranged during the course of this experiment by an accident, but this close coincidence certainly rendered a repetition of the inquiry unnecessary. On these experiments, our good-natured cotemporary before referred to remarks: "The Sub-committee did not make one experiment on this subject; they decide upon the uncomfortable experiments of the preceding investigation, &c." Which uncomfortable experiments, as he facetiously (?) terms them, were quite as directly to the point as if they had been intended solely to apply to it, to the exclusion of all other deductions.

250° Fah., a portion was thus forced out, in the liquid state, at 223° Fah. The entire series of conclusions drawn by the Committee will serve to indicate their train of experiment, for the numerical results of which we must refer to the Report itself.

"The conclusions deduced from the foregoing experiments on metallic alloys may be thus stated :

"1st. The impurities of common lead, tin, and bismuth, are usually not such as to affect materially the fusing points of their alloys.

"2nd. When mixed in equivalent proportions, tin and lead formed alloys, not presenting the characters of distinct chemical compounds, in definite proportions. The alloys between the range of one equivalent of tin to one of lead, and one equivalent of tin to six of lead, varied considerably in the interval between the temperature of commencing to lose fluidity and that at which the temperature of a thermometer, immersed in the solidifying metal, became [for an instant] stationary. These different alloys produced nearly the same stationary temperature in a thermometer plunged into the solidifying metal.

"3rd. Fusible metal plates, covered by a perforated metallic disk, and placed upon a steam-boiler, show signs of fluidity at the disk before the steam has attained the temperature of fusion of the alloy of which the plate is composed. This fluid metal oozes through the perforations in the disk, and the plate thus loses much of its substance before finally giving vent to the

steam.

"4th. The under parts of the plate are not kept from fusion by a protecting film of oxide there formed.

5th. The thickness of the plate is not important, provided only that it is sufficiently strong to resist the pressure of the steam at temperatures below its point of fusion.

"6th. The temperature at which the plates are cast, and the rate of cooling of the cast metal, do not affect the temperature at which the plates give

vent to steam.

"7th. The effect stated in conclusion third is explained by the nature of the alloys used, which are formed of portions of different fluidities; the more fluid parts are forced out by the pressure of the steam, leaving the less fusible. These latter, in general, are burst, not melted.

"8th. By pressure in a receptacle provided with small openings this effect of separating the differently fluid portions of an alloy may be imitated.

"9th. Fusible alloys, used to indicate the temperature of any part of a steam-boiler, should not be exposed to the pressure of the steam; at least, not in such a way that the separation of the differently fusible constituents of the alloys may be effected."

We shall return to this subject under the next head, to which we now proceed.

2nd. Explosions produced by the presence of unduly heated metal within a boiler.

It was first observed, we believe, by the chemist Klaproth, that when small drops of water were in succession thrown into a red hot iron spoon, the first drops evaporated very slowly, and succeeding ones disappeared more rapidly as the vessel cooled. These observations, and others of an analogous sort, have been supposed to contradict the conclusion that highly heated metal can produce steam rapidly, when water was thrown upon it. M. Arago, in his Essay upon the Explosions of Steam Boilers, considers this as a capital difficulty to be

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