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REPORT OF EXPERIMENTS ON THE EXPLOSIONS OF STEAM-BOILERS,

99

In the last experiment, the glass window at the fire end of the boiler blew out with a quick, sharp report, as loud as that of a musket; the fragments of glass, from a hole in the centre of the plate, were projected through a window, about three feet from the boiler, and could not be found. The number for twelve atmospheres is placed opposite to this experiment, as being an approximate result. In the act of observing the gauge, the glass burst, and the mercury at once fell: the number of inches at which the mercury had certainly risen, and above which it was, by an undetermined quantity, not however very considerable, was noted; and from this the pressure given in the table is calculated. Here explosive steam was generated by the injection of water upon red-hot iron, and in a time not exceeding one or two minutes at the most, the interval between the last stroke of the pump and the explosion not having been sufficient to note the height of the gauge; the experimenter being at the pump, which was adjacent to the gauge.

By comparing the temperature of the steam in these experiments, with its observed pressure, it will be seen, that in not one of them was water enough injected to give the steam a density even approaching to that corresponding to its temperature: for example, 336° Fabr., should give a pressure of nearly 7 atmospheres, instead of 3:3, the observed pressure; 388° should give more than 14* atmospheres, instead of 8.2 and 4480; about 27} atmospheres, instead of 10. The vio. lence of the effect was not, therefore, carried as far as it might have been, the metal not having been cooled down as far as it might have been, to produce the greatest effect; and yet within two minutes tlie pressure was changed from 1 to 12 atmospheres.

The rise of temperature shown in the first column serves to prove, that by successive introductions of water the metal was not so far deprived of heat as to be cooled towards the point of maximum vaporisation, but that the results were obtained with metal heated to redness.

A similar experiment to these was made by our countryman, Perkins, but surcharged steam being present in the vessel into which heated water was forced, it was to the action of this that he attributed his result. This opinion will be examined subsequently, but the attributed source of action was present only in a very attenuated state, if at all, at the beginning of each experiment made by the Committee.

The repetition and extension of the experiments of Klaproth was one of the most laborious of the undertakings of the Committee,

and the results will be found in a future article of the Report.

III, To ascertain whether intensely heated and unsaturated steam can, by the projection of water into it, produce highly elastic vapour.

The supposition that water, thrown into hot and unsaturated steam, is flashed into highly elastic vapour, forms the basis of the theory of the explosion of steam-boilers of our countryman, Perkins; a theory which has been embraced by many; and which, though shown to be contrary to the deductions from the well-established laws of heat, is not now without its advocates. It seemed to the Committee interesting to appeal to direct experiment upon this point, and thus to ascertain whether any circumstances, not embraced in the general view of the theory, existed ; or whether all the circumstances had been rightly estimatec, ml dtke cocia sions drawn from the application of the general laws heat would be confirmed. Being unwilling to incur any considerable expenditure in this branch of their inquiry, the ex. periments were rendered uncomfortable beyond any thing which occurred in their other researches. The means of producing the unsaturated steam were these : a row of bricks was removed from the top of the furnace, and near to the boiler, thus laying bare nearly half the convex surface of the latter (five inches from the top). By building on the sides of the top of the furnace, with bricks, loosely arranged, a space was formed for placing fuel having the boiler for its bottom, and bounded by the bricks on its sides. A cap of sheet-iron above served to promote the draught, and toca rry off much of the de. leterious gas produced by the charcoal used as fuel. The fusible plate apparatus was removed from the boiler, to prevent injury, and the safety-valve was surrounded by a tin to keep the fuel from contact with the valve. By filling the boiler about half full of water, and applying heat below to raise the water to any required temperature, the upper half of the boiler would be filled with steam of an elasticity due to that temperature, this elasticity being measured by the gauge. Fire being now placed upon the top, would heat the metal of the upper half of the boiler; and this, by communicating its heat to the steam, would surcharge the latter. To mea. sure the temperature thus acquired by the steam, as well as that of the water below it, thermometers were placed in the iron tubes already described; the mercury was removed from the tubes, except enough to corer the bulbs of the thermometers, so that the temperature shown by them might be, as nearly as possible, that of the steam by which the shorter tube was surrounded, apd of the

Arago and Dulong,

100

REPORT OF EXPERIMENTS ON THE EXPLOSIONS OF STEAM-BOILER3.

water into which the longer tube dipped. The scales of these instruments were proteeted from the fire by surrounding them, at some distance, by tin plates. The scales were of seasoned hox-wood, the refinement of a correction for the errors of the instruments was not considered to be at all required by the nature of the research, the results of which errors even a few degrees of temperature would not materially affect. In the final experiments on this subject, the thermometers, with metallic scales, and surrounded by water, were put in place. The apparatus for injecting water consisted of a tube attached to the stop-cock v, fig. 1, on the back head of thc boiler, and which communicated with the forcing-pump; the tube terminated in a spherical segment, in which fourteen holes, each of the size of a cambric needle, were made; through these the water was forced in spray. By examination it appeared that the small stream, from the highest hole, struck the top of the boiler near the safetyvalve; that two or three struck the front head; two or three the water in the boiler, near the back head, leaving from seven to nine apertures, the water from which crossed the steam-chamber in an inclined and very effective direction. The effect of the streams from the three or four apertures first spoken of, would be, if they were not taken up by the steam, to vitiate, in degree, the experiments, by striking the top and end of the boiler. With the openings, thus described, the first day's experiments on this subject were made. The heat of the surcharged steam could not, with the arrangements then provided, be raised above 4840. The method of experimenting having been the same as was subsequently used, may as well be stated in this place. The fire having been applied below the boiler, the water was heated to a temperature corresponding to from one and a half to two and a half atmospheres; the coals were then, in part, removed to the top of the boiler, fresh fuel being supplied below: the effect of the heat applied above was soon visible upon the thermometer in the steam, and upon the gauge. When the temperature of the surcharged steam sufficiently surpassed that of the water, as shown by the larger thermometer, the injection of water was commenced, the injection-pipe being carefully kept cool by wet sponges and cloths. The temperature of the thermometers in the water and steam were noticed both before and after the injection by one experimenter, while a second made the requisite number of strokes of the forcing-pump, observed the indications of the steam.gauge, and when the experiment was concluded, gave the quantity of water used. The temperature of the air in the gauge was noted from time to time. The apertures in both the heads were secured

with metallic plates, to prevent leakage through them.

On the second day, six of the fourteen small holes were plugged up, that the source of error, already mentioned, might not exist. The temperature attained by the surcharged steam was 440°, at, and below which, experiments were made. The general nature of the results, obtained on the first and second days, coincide, allowing for the difference of circumstances, so entirely with those of the final trial, when a satisfactory temperature was obtained in the surcharged steam, that it would be uninteresting to detail them. The same remark may be made of subsequent trials.

As the quantity of water thrown in during all these experiments was small, it was considered advisable to increase it, in order that more marked effects might be obtained; this was done by removing the pierced head from the pipe, thus delivering nearly the full capacity of the pump at each stroke. The quantity of water thus injected through the steam by each stroke of the pump was, at a mean, half a fluid ounce. No heating of the injection-water was required, as the heat necessary to raise water from the temperature of the experiments to the boiling point was but a small fraction of that required to convert it into steam.

In the last day of trial the heat of the top of the boiler was so great and so long sustained, that the thermometer in the water became, in the course of the experiments, for reasons which will be stated, comparatively useless, as an indicator of the temperature of the water. The following tabular view of the results of the experiments is extracted from the minutes. The first column of the table contains the temperature of the surcharged steam, previous to the injection of water in any experiment; the second column that after the injection: this comparison being made to ascertain whether the heat supplied was, or was not, sufficient to make up for that consumed in vaporising the water thrown in. The third column shows the quantity of water injected; the fourth the height of the gauge before the experiment; the fifth the height after the experiment; the sixth the temperature of the gauge; the seventh and eighth, the pressures in atmospheres, calculated from the height of the gauge, and the temperature of the air within it, before and after each experiment. No notice is taken of the temperature of the scales of the thermometers, it having varied but 100 Fah. namely, from 86 to 96o.

The first experiment is introduced, to show the temperature of the water within the boiler, before the long-continued heat had sensibly affected the indications of the thermometer,

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REPORT OF EXPERIMENTS ON THE EXPLOSIONS OF STEAM-BOILERS.

101

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0 21:17
65 5.72

For comparison, no water injected.

Water in the boiler, 318° Fah. 2 21.30 21.25 66 | 5.85 5.80 3 21.50 21.50 6:15 6:15 Gauge stationary. 7 21.52 21:47 6.21 6.07 21.80 70 6.65

Temperature of air in gauge

noted between two experiments. 3 21.80

6.65

Gauge fell slightly, then rose to

original level.
64 21.80 21.70 6.65 6.48
10 21.80 21.65

6.65

6:41 13 21.80 21.60 6.65 6.34 21.90

6.82 21.90 21.85 6.82 6.74 Rose again immediately to 21.90. 14 21.90 21 70 6.82

6:48 Fell nearly .2 inch. Note, 533° is,

according to the formula of Arago and Dulong, the temperature of saturated steam of more than sixty atmospheres.

At the close of these experiments, the metal was, in many places, but little short of a red heat, visible in day.light.

The precise state of things in a boiler, of which parts are unduly heated, was represented in these experiments; there was the surcharged steam, and heated metal ready to give up its heat to replace what might be ab. sorbed in the conversion of the water injected into steam. This latter circumstance ren. ders the case different from that contemplated in the deductions of theory which have been brought to bear upon the question. The greater or less intensity of the heat afforded by the top and sides of the boiler would necessarily modify the effects observed, by the injection of any given quantity of water; this is observable in the numbers given in the table, where although the greater quantity of water injected does not fail in two consecutive experiments to show a greater depression of the gauge, yet in distant experiments the same is not the case. We see that in no case was an increase of elasticity produceıl by injecting water into hot and unsaturated steam, but the reverse, and in general that the greater the quantity of water thus introduced, the more considerable was the diminution in the clasticity of the steam. The quantity of water injected was from 3:5 to 24:3 cubic inches. The immediate rise of the gauge after each experiment, shows how rapidly heat was supplied by the sides of the boiler to the steam within.

That the steam was highly surcharged with heat, appears by comparing the pressures corresponding to tb etemperatures with those

given by Dulong and Arago for saturated steam. For example, the pressure shown by the gauge when the steam was at 506° Fah. was 6:15 atmospheres, while the table just referred to gives for this temperature a pressure of forty-eight atmospheres. The temperature was carried to 533° Fah. when the pressure shown by the gauge was 6.82 atmospheres, while saturated steam at that temperature would have had a pressure of more than sixty atmospheres.

In order to ascertain whether the thermometer relied upon to give the temperature of the steam was affected, if at all, in excess or defect by the conducting power of the metal ; the temperature of the boiler just beyond the tubes was taken, as nearly as was practicable, by a thermometer R, fig. 1, dipping into a clay receptacle, upon the top of the boiler. This thermometer did not rise above 4050 Fah.; its distance from this source of heat was ten inches, and that of the iron tube inclosing the thermometer, six and a half inches. Supposing the temperature stationary on top, the temperature of the metal of the top of the boiler near the tube of the thermometer would have been 4790,* show

* If we suppose the heat of a small bar of metal, cut from the top of the boiler, to have been derived by the conducting power of the metal alone, the heating effect of the steam within being neglected, and further, that the temperatures of the bar had become constant, then the ratio of the excess of the temperature (y) of any point at a distance (x) above the iemperature of the air, to that (y') of any point at a distance (w'), is given by the proportion,

y?:y:: log.x : log. x'. In the case before us, y=405 — 80 = 325o, X

If we

102 REPORT OF EXPERIMENTS ON THE EXPLOSIONS OF STRAM-BOILERS. ing that it tended to carry off heat from the The answer to this question is given by the thermometer, which, if at all affected by the experiments just detailed ; and as they estametal above it, showed too low a temperature blished the negative in relation to the surfor the steam in contact with it. The tem- charged steam becoming saturated, there was perature of the source of heat would have no necessity for a repetition of the experibeen from these data, 582° at the extreme ments to ascertain the precise temperature of end of the part covered with fuel, which was the water in the boiler. When fire was apof course at a lower temperature than the plied to the top of the boiler, the water within middle portior

was at 3189 Fah.; a moderate fire was kept On examining the apparatus after the con. up below, and one so nearly uniform, that clusion of the last day's experiments, it was great variations from that temperature could found that some of the putty used in tighten- not have taken place, and which the results ing the lower joint of the thermometer in the satisfactorily show did not occur. water had been softened by the heat, and assume that during the experiments the temhad flowed into the tube, thus affording a perature was 30840 Fah., a remarkable cordirect communication between the steam and respondence will be found in the observed the bulb of this thermometer: this circum. pressures, and in those calculated on the supstance accounts for the instrument being position that this steam was expanded by affected in this day's experiments and not in heat, as a gas would have been, without any the preceding ones.

addition of water. The table below gives the IV, The next query may be thus stated : temperatures of the surcharged steam obwhen steam, surcharged with heat, is produced served at different times during the course of within a boiler by the contact with heated the experiments; the pressure shown by the metal, does this steam remain surcharged, or gauge at that temperature; the pressure which does it take up water from contact with that in would have been produced by heating steam the boiler, and become saturated steam ? If at 308° to the temperatures given in the the latter supposition be correct, at what first column by the mere effect of expansion; pressure and temperature with regard to the and the pressures of saturated steam at the temperature of the surcharged steam, and to different temperatures. that of the water on which it rests?

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REPORT OF EXPERIMENTS ON THE EXPLOSIONS OF STEAM-BOILERS. 103 acquiring from it the water necessary to comes Auid before the rest, and gives way, convert it into saturated steam, but retain- the rest being in the sandy state, just spoken ing its surcharged state. There is nothing to of, the particles seem to act like those of warrant the belief that any of the surcharged

sand in a similar case, and to oppose an steam was condensed by the water.

effective resistance to the pressure of the

steam ; these facts will be further developed V.-Inquiry in relation to Plates of

in the examination of the application of these Fusible Alloys.

plates. It is well known that one of the most The stationary points, when taken with scientific nations of Europe relies, particu

due reference to the state of the metal at the larly, as a means of safety for steam boilers, time, afford so many approximate marks by on the use of plates of fusible metal. The which to compare together the fusibilities of plates are alloys of tin and lead, or of these the plates, and to ascertain whether they bear two metals with bismuth, the proportions of

a due relation to each other, when fused, in the component metals regulating the point at place upon the boiler; and to study the alloys which they fuse. In France these alloys are

themselves, In composing alloys of the prepared at the royal mint, where plates made metals, before referred to, the tin was fused from them, or ingots of the alloys, may be first at as low a temperature as possible, then purchased for use. The examinations which the bismuth and lead added, the heat being must have been made to determine the pro- kept up; these metals were readily taken up portions of the metals necessary to produce by the liquid tin, and were thus little exposed an alloy fusing at a given temperature, and

to oxidation: the surface of the alloy was the circumstances of fusion, have not, as far always protected by a stratum of oil. The as the committee know, been made public. metal was constantly stirred to promote the A table of the fusing points of different uniform diffusion of the different metals alloys of tin, lead, and bismuth, &c., was throughout each other. drawn up by Parke, from experiment, and is The alloy being liquid, a thermometer, of contained in his chemical essays, vol. ii. p.

which the errors had been carefully ascer615. This table was made the basis of the tained, was plunged into it, and the fall investigations* undertaken by the committee, noted until it reached the lowest point; the but they soon found it convenient to depart, rise to the stationary point followed, and at more or less, entirely from it.

this the thermometer usually remained for The method employed by Parke for deter- such a length of time, often some minutes, mining the fusing point of a metal, or rather as to render any error of observation unnethe solidifying point of the melted metal, was cessary. Some of the alloys have no staingenious. On melting a metal, and allow- tionary point, properly so called, and the ing it to slowly cool to the point of congela

beats of a second's pendulum were used to tion, and observing a thermometer plunged

determine the rate of their loss of heat. in it, a rise of temperature, and then a When the quantities of metal used were instationary point, is observed; this is a point considerable, the heat was observed to be where a change is going on, by which the

carried off so rapidly as to lower, or entirely heat given out in the change is equal to that to destroy, the stationary point: to avoid of which the metal is robbed by the sur

this, the crucible containing the alloy was rounding medium. This point usually coin.

placed in a second one, the edges of the cides with the passage of the metal to the

former resting on the middle of the sides of solid state, from what may be either the

the latter. The quantity of metal used was liquid state, or a semi-fluid state, similar in

never less than between five and six ounces, aggregation to sand; sometimes the alloy is troy. solid throughout, before the stationary point

The stationary point being at the passage arrives; and sometimes there is more than

of the liquid metal to the solid state, or at one such point.

some interior change of the 'solid itself, the The stationary point is not that at which thermometer was entangled in the metal; and the alloy, when used as a fusible plate for a

in moving the alloy, to re-melt it, the instruboiler, gives way; the plate being covered by ment was endangered.* This was remedied a perforated brass disk, to prevent its being by the use of a small cylinder of very thin pressed outwards before fusion, and so re

sheet-iron, containing mercury. This cylinduced in thickness ås to burst, the metal is

der was placed in the alloy, and filled up to pot forced out through these openings until

the surface of the metal with mercury, and perfectly fluid; if any part of the metal be

the thermometer could now be readily placed

* Although the instrument was frequently used At the time these experiments were made, the in determining the stationary points, no permapåper of Rudberg Ann. de Chimie. et de Phys., nent changes in the indications of the iustrument, vol. 48, had not appeared.

such as was noticed by M. Rudberg, took place.

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