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TREASURY DEPART

114 REPORT OF EXPERIMENTS ON THE EXPLOSIONS OF STEAM-BOILERS.

fect. The disk which covered the fusible REPORT OF EXPERIMENTS MADE BY THE COMMITTEE OF THE FRANKLIN INSTI- plates prevented in part the loss of heat from OF PENNSYLVANIA

surface. ON THE EXPLOSIONS OF STEAM-BOILERS, AT THE "The plates which were first cast were in. REQUEST OF THE

tended for low pressures, as most convenient MENT OF THE UNITED STATES,

for experiment, they were fifteen hundredths

of an inch in thickness. The obserratio S (From the Journal of the Franklin Institute.)

made upon the manner in which they acted (Continued from p. 106.)

when in place upon the boiler, led to the The second part of the inquiry relates to q'estion of the effect of varying the thickness the action of fusible plates when in place on upon their use. When a plate of sufficient th: boiler; it supposes proper alloys, fusing thickness to prevent its giving way to fresat required temperatures, to be composed, and

sure, verges towards its point of fusion, the then sudies the causes, modifying the action top part, which is in contact with the metal of them when placed on the boiler. In the disk, melts, and fows over the holes in the first apparatus for the use of these plates the disk; sometimes it accumulates until the attempt was made to introduce them within liquid rolls off the plate. The temperature the boiler, but the difficulty of replacing a rising, a small pellet of the more perfectly plate which had fused by another plate, led fused parts is thrown out by the steam, the tu the abandonment of this apparatus. The flow of which is instantly checked; this is opening made in the builer, when the plate repeated frequently, until a breach through was withdrawn, was so great that the contents the plate is made, and the uninterrupted fvw of the boiler were violently discharged through of steam takes place. If the plate be removed it before the operation of replacing the plate at once, a very small hole appears, which could be effected. This observation has a would gradually have been widened by the bearing upon the plans for making large action of the escaping steam, probably before openings in boilers of full size to avoid the entire fusion of the plate. The under explosions.

surface of the plate appears oxidised, and the The apparatus finally used was a sliding- fusion to have taken place at the top: the plate, moving in a groove upon the upper side plate has contracted in its dimensions, and of the boiler, as shown in figs. 1 and 3, where the periphery of the upper surface has lost its $ represents the slide moved by the lever yo ; circular figure, which is tolerably well prein the middle of the slide was an aperture served by the lower surface. To give some slightly conieal, for receiving the fusible plate, idea of the extent to which a plate such as this aperture was eight-tenths of an inch in just supposed may lose its substance before diameter. By means of the lever, the plate giving way, two measurements are subjoined. could be brought over an opening in the top Before fusion the diameter of the upper surof the boiler, or the solid part of the slide face of the plates was eighty-four hundredths might be made to cover the same opening. of an inch; the lower diameter eighty-two The fusible plate was covered by a disk of hundredths of an inch : the thickness of the brass, the edge of which projected over the plates, fifteen hundredths. After the plate plate, and l'ested upon the slide. There were had given way, the diameter of the hexasix holes drilled through this plate, each be- gonal figure into which both the surfaces had ing about nineteen hundredths of an inch in passed, was about seventy-nine hundredthis diameter. To retain the slide in its place, for the first, seventy-four hundredths for the when pressed from below, and to retain the second; the diameter of the lower surface, fusible plate when in a similar situation, the which was still nearly circular, was, for the forked stem L, pressed in the former position first, seventy-six hundredths; for the second, by one leg upon the slide s, in the other by sixty-nine hundredths; the thickness of the the other leg upon the disk covering tlie fusi- first was about twelve-hundredths, of the seble plate; the upper end of the stem entered cond, one-tenth of an inch ; the thickness -a cavity in an adjusting-screw t, passing not being uniform in all parts. The first through the gallows u; by this means allow- plate had lost, therefore, nearly three-tenths, ance could be conveniently made for expan- and the second half of its substance, without sion. The lever for moving the slide rested, allowing the passage of steam. when the aperture in this latter for receiving The observed oxidation of the lower side of the fusible plate coincided with the opening the plate led to the supposition that it might in the boiler, against an upright, projecting retard the fusion of the plate, but no confirmfrom the top of the boiler, and serving as a ation of this view was given by comparative stop. By the use of this apparatus, the experiments with plates of which the lower plates were applied very readily, were re- surface was brightened, and of others in moved when fused, and the opening into the which the same surface was highly oxidated, boiler closed with so much, dispatch, as to the thickness in each case being the same. prevent the foaming within from taking ef- In the course of the experiments ou the

REPORT OF EXPERIMENTS ON THE EXPLOSIONS OF STEAM-BOILERS. 115 effect of oxidation, the plates were much re- tuted. The steam was again retained, and dured in thickness by filing away the under allowed to rise in temperature, the new plate surface, and the fusion of the thinner plates pushed to its place, and the operation retook place at points so much lower than those newed. This course was continued until the at which the thicker plates of the same alloy alloy, fusing at the highest point of those pregave way, so as to require an examination of pared, had been used, or until the limit of the the cause.

elasticity of steam, which could be produced Before proceeding with further detail, it in the actual condition of the boiler and state may be well to state the general method of of the fire, was attained ; steam was then let experimenting upon the plates. The station. off, water thrown into the boiler, and a new ary point of an alloy having been determined, series commenced. The tables which will be and remarks made as to its point of fusion, given required many days of trial and of plates were cast from it; and one of these close attention. being placed in the opening in the slide of To try the effect of thickness on tbe fusion the apparatus already described, was covered of the plates, three different thick nesses were with the pierced disk, and the slide moved so cast of each of the alloys used; the first, or as to bring the plate over the opening in the thickest, was fifteen-hundredths of an inch boiler. The steam was now raised, the tem- thick; the second, eight-hundredths; and the perature being noted from time to time, until third, four-hundredths. There were five difthe plate gave way; steam was then let off to ferent alloys of tin, lead, and bismuth, comkeep the temperature from rising; the plate, posed; the stationary points of which, and which had just fused, removed, and one of an the points at which they gave way in the alloy, fusing at a higher temperature, substi- boiler, appear below.

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The plates of Experiments 1, 2, and 3, were exposed to pressures tending to render them of less than one atmosphere; ) and 3, the two extremes of thickness, show a great uniformity in the point at which they give way, and render it probable that some flaw, in casting the plate number two, caused its fusion at a lower point than that of either of the others; we see, too, that at these low pressures the fusing point in the boiler coincided very nearly with the point at which the alloy was a soft solid in the crucible. In this case the thinnest plates, when properly cast, were probably thick enough to withstand the

small pressure to which they were exposed, and therefore did not give way at lower temperatures than the thickest, each attaining the temperature at which they were soft solids.

The next series, Nos. 4, 5, and 6, with a less fusible alloy, show, first, that the thin nest plate was too feeble to resist the pressure of steam, and gare way before the metal lost its colidity ; second, that the plate, eighthundredths of an inch, was probably defective, as it gave way at a lower temperature than the thinner plates of No. 4. No 6 presents a curious fact; the point of yielding of the REPORT or BXPERIMENTS ON TAE EXPLOSIONS OF STEAM-BOILERS.

116

plate, given by four experiments, is actually above the point at which the alloy from which it was composed became liquid : this would appear inexplicable to one who had not attentively observed the mode of fusion of these thick plates, and would lead to the suspicion of error. The observation of the point at which the alloy became liquid, was, however, deduced from three trials; and four experiments, with the plates in place, are given, the extremes differing but three degrees. The explanation is to be found in the mode of fusion already spoken of; the more liquid parts of the alloy are forced out, the less fusible remain, and if strong enough to resist the pressure, the process goes on; this takes place unequally in different alloys. The importance of attending to such indications is obvious.

In the next series, the first thickness seems to have been decidedly too weak, and the second to have been hardly sufficient, while the third exhibits a point of fusion when the metal was in a softened state.

In the remaining experiments, both thick: nesses were too inconsiderable to sustain the pressure, as appears by comparing the points at which the plates gave way with the stationary points. Something of this kind seems to hare been deduced from practice in the use of these plates in France, for the last royal ordinance, in relation to the means of safety to steam-boilers, prescribes for the plates a thickness of nut less than nine-sixteenths of an inch, making of them fusible plugs rather than fusible plates.

Experiments were subsequently made on plates of greater thickness, the use of which led to an interesting termination to this series of experiments. Before, however, stating the results thus obtained, some further experiments with the plates just considered will be described. These inquiries were directed to the effect which would be produced by the mode of casting the plates upon their fusibility; it being not improbable that rapid cooling might so modify the physical properties of the alloy as to change the fusing point from that of the same alloy when slowly congealed.

As low pressures afforded the most easy means of determining this point, plates were cast from the alloys of series No. 1, No. 2, and No. 3, and tried, in place, upon the boiler. Some of the plates were cast from metal at a high temperature, and the mould as cold as the perfect casting permitted; others, of the same alloy, in a heated mould allowed to cool slowly; and others from metal heated to a temperature as little above the point of fusion as possible. In the case of the higher temperatures, care was taken

not to raise the heat so far as to oxidate ra. pidly either of the constituents of the alloys, thus changing the fusing point. A comparison of the results obtained showed no greater differences than those which have been seen to occur between plates similarly cast, and from the same alloy; and the conclusion derived was, that the mode of casting has no effect on the fusing point, which is appreciable in this mode of applying them. The French instructions expressly recommend to those who make or use boilers, to obtain plates in preference to the fusible metal in ingots; on the ground that it will be found difficult to procure plates of the same fusibility with the ingot, from that form of the alloy. This remark led to the experiments just referred to, and the explanation of it which they give, refers to the undue heating of the alloy in the casting of the plates, since they show that the particular mode of casting produces no difference worthy to be regarded in a practical point of view.

Plates were now cast quite thick, viz. onefourth of an inch, of the alloy of eight parts of bismuth, eight of tin, and seven of lead; this alloy being intended to give way at a temperature corresponding to about one atmosphere of bursting pressure. The alloy was completely liquid at 275° Fah, and solid at 2510 Fah., * when examined in the crucible. The heat was raised as slowly as possible, so as to permit the full effect of the temperature indicated by the thermometer; the observations recorded are as follows. (See top of next page.)

The thermometer on top of the boiler dipped into the mercury in a small cistern, made by inclosing a space on the top of the boiler with clay; so that the top of the boiler formed the bottom of the cistern. The first plate having failed to give way until the temperature within the boiler was 21° above that at which the alloy, of which it had originally been composed, had been fluid, was examined with great care. The plate had decidedly given way to pressure, and not by fusion ; it had lost its metallic lustre at the side where it was torn; yielded readily to the nail, which scraped off small particles. A piece of the plate being cut off and laid upon the top of the boiler, remained solid, though the portion which had oozed out was perfectly fluid near the same spot. The same remarks apply, generally, to the second plate. They afford a solution of the perplexing circumstances which liad occurred throughout these experiments, and which had led to so many trials to discover their cause.

• This alloy had no stationary point in passing from the liquid to the solid state : but some internal change in the solid al about 206°, produced a rise and statiovary point at 208o.

REPORT OF EXPERIMENTS ON TEE EXPLUSIONS OF STEAM-BOILERS.

117

Thermometer in Therm.
Steam.

on

top of Therm. Scale. Boiler.

Pres.
sure.

REMARKS.

Fabr. Fahr. Fahr.° Alinos.

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Plate fth of an inch. Metal stands fused in the holes of the brass disk covering the susible plate.

Steam issues in a very small struam through chinks between the fused metal and an unmelted part within.

Steam issues as before; no clear passage through the plate. Steam kept for a long time at this temperature. Six minutes elapsed in raising temperature 4 degrees.

Plate gave way, affording a free passage to steam.

A second plate of the same composition and thickness, put in place; fuid metal stands in the holes of the cap.

Metal which has oozeil out remains in a fluid state upon the sliding plate of the apparatus.

Plate gives way, torn in a thin part.

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The portions of the metal which oozed out Fah., and a portion of that from the second from these two plates had their fusing points plate was Auid at about 2354° Pah. The taken, by gradually raising their temperature parts which were left of the first plate were a in a bath of oil, while the alloy rested on a soft solid, at 2994?, Auid at one edge, at small shelf

of copper, wholly immersed in the 312', and entirely fuid at 345o. oil. The first portions of Auid metal which The portions left of the second plate lost had oozed from both the first and second their cohesion, and could be broken by pound plates, melted at between 221° and 223° ing into small particles or grains, at 3004° ; Fah , being solid at the lower, and perfectly and the whole was fluid at 356° Fah. A fuid at the higher, of these two temperatures. comparison of these results appears in the The second portion which oozed out from the annexed table. first plate fused at between 230° and 2330

First ooze.
Second ooze.
Residuom.

Entire plate

before experiment.
Finid.
Finid.
Fluid.

Fluid.
First plate

223°
233°
312 a 345

254 a 275 Second plate 223 235) a 241)

356 To pursae this subject further, by the clue lead, one of tin, and one of bismuth, is fluid thus obtained, only freeing the different at 2731° Fab., and that of one atom of lead, oozes from accidental admixture, a small iron one of tin, and two of bismuth, at 2199 Fah. cylinder was made, closed at one end, and These experiments the Committee deem perforated near the closed end with a number conclusive in regard to the use of fusi»le of minute holes, not larger than the stem of a plates in the ordinary way; and they conceive common pin. Into the cylinder was fitted, that substituting fusible plugs of greater pearly tight, an iron piston, with a rod, to thickness, say half an inch, as has been diapply pressure. An alloy having been made recteů by a recent ordinance in France, would and introduced into the cylinder, the whole not serve as a remedy to the defect thus excould be heated in an oil bath to any desired posed. The true remedy is to be sought in temperature; and pressure being applied to inclosing the fusible metal in a case, in which the piston, the liquid parts would ooze out it shall not be exposed to the pressure of the through the small apertures near the end of steam, but only to its heating effect; the the tube. The first alloy experimented upon more fluid parts of the metal will then not be was the same in composition with that just exposed to be forced out of the mass; and referred to; being composed of eight of bis- the whole will become fuid as if exposed to muth, eight of lead, and seven of tin, by heat in a crucible. With this view of the weight. This alloy was fluid at 2544 Fah. subject, trial was made of an apparatus deAt a temperature of 229°, some drops of scribed by Professor A. D. Bache, in the fluid metal were forced out by pressure, and Journal of the Franklin Instilule, for at about 2397° other portions were forced October, 1832, under the title of an "alarm out. Both melted at 227° Fah. The pos. to be applied to the interior flues of steamtion left was a soft solid at 2761° Pah.; boilers.'* This apparatus is obviously as fuid at 2901 The alloy of one atom of applicable to a common boiler as to‘one with

• This paper was published in 1832, and the experiments of the Committee were made in 1833-4.

118

REPORT OF EXPERIMENTS ON THE EXPLOSIONS OF STEAM-BOILERS.

interior Aues; the following description of it is given in the journal:

A tube of iron, or copper,” according to the material of the boiler, “ closed at the lower end, passes through the top of the boiler, its closed end reaching the fue to which it is attached." -“ This tube, it will be observed, affords a ready access to the flue, to ascertain its temperature, without any restraint from packing.”

'_"A mass of fusible metal placed at the bottom of the tube," "will become fluid very nearly as soon as the fue takes the temperature of fusion of the alloy."'-" To show when the metal at the bottom of the tube becomes fluid, a stem is attached with a cord and weight,” " with a lever and weight.”'-" The weight and longer arm of the lever descending, may be made to ring a bell, or, by appropriate attachments, to turn a cock, permitting just enough steam to issue to give the alarm, and then to be closed at once. A projection on the lower end of the rod prevents it from being drawn from the metal until this latter is fused, and by widening the lower part of the tube, making it slightly tapering, the metal is kept from being drawn out by the rod."

or

sponding section of its flue; EH represents a tube closed at the lower end, which is at. tached to the upper side of the flue. The mode of attachment by a projection on the tube and a ring screwed to the fue, is shown in the figure, as also the stuffing-box RS, through which the upper end of the tube passes. The lower part Hl of the tube is made tapering, to retain the fusible metal. KL is the stem, the lower part being inclosed by the fusible metal, the upper part attached by a chain to a lever KP. The weight M draws the rod KL upwards, and on the fusion the alloy H I carries the lever below the bell N, which being attached to a spring, rings an alarm."

The form of this apparatus, which was subjected to trial by the Committee, was essentially the same with that described. Que of the tubes in which the thermometers were ordinarily placed, was used to contain the fusible metal, and as giving the more severe test, the short one entering only into the steam was selected. For the convenience of removing the metal, it was placed in a metal. lic case, fitting loosely into the iron tube, and having a wire attached, by which it could be drawn out of the tube. This certainly diminished the sensibility of the apparatus, particularly as the case was quite as thick as the inclosing tube, and as there was a small space between its convex surface and that of the tube; it was required, however, for the convenience of the experiments.

The results of the several trials are contained in the following table. The temperature was registed by the adjoining thermo. meter dipping into the water of the boiler, and already often referred to; it was raised as rapidly as possible in all the experiments except the first. The first four trials were made on an occasion specially devoted to this purpose, the last two were made incidentally when upon another subject.

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Stem rises. No particular attention paid to raising the temperature

rapidly. Stem rises. Steam raised rapidly. Metal drawn out and suffered to cool, re-deposited cold in tube. Steam

at 238', and raised to 271' in 2 minutes.
Stem rises.
Metal drawn out and cooled. Steam at 250°, when metal was re-

placed. Steam raised to 274° in 3 minutes.
Stem rises.
Melal had not become solid again. Steam let off rapidly.
Multed below this temperature.
Stem rises. Metal remains a soft solid, so that the stem can be drawn

out until 240°.

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