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Now, taking the ton of coals at 24 coals per day. The work done by the bushels, 26 tons 864 bushels, and boilers of the Great Western, in the bush. per day

evaporation of water, is just 10 to 1; but 7200 5 X 1440

102 cubic feet of

the effect of the steam on the piston is 864

only as 5 to 1. The quantity of water

consumed at each stroke of the cylinder per day

is not quite exactly the same in both en

720 water per bushel ; •5 x 1440

gines, as -5 has been substituted for · 493 105

of a cubic foot per minute, in the Cor68) bushels, or less than 3 tons of nish engine.

bush,

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The conditions were approximately taken 14 lbs. we shall have 21 lbs. resistance from practice, without reference to this on the under side of the pistons of the point, and the circumstance was not no Great Western's engines, and conseticed at first.

quently 1th part of 800 horses power, or The value of the cylinder vacuum, and 133 horses power resistance against the also the value of the friction air-pump piston. The allowance is less in the power absorbed, must be estimated, to Cornish 'engine, on account of the pause obtain the net horse power, according to between the strokes. The friction alloweach person's views; and it is as easily ances must be made at pleasure. I conmanaged with the total steam pressure ceive the mean power in crossing the expressed as horse power, as with the Atlantic will not reach 600 horses power. pressure in lbs. per square inch. Taking I remain your obedient servant, the condenser at $ lbs., and the mean

S. difference between it and the cylinder at

BY MR.

ON THE CAUSE OF EXPLOSION IN STEAM-BOILERS, AND THE REMEDY.

WILLIAM SAMUEL HENSON, [We have in a former Number (493) the safety-valves at the time of the exdescribed an improved mode of working plosion, showing the valves to have had steam expansively, which forms the most an insufficient area, being only from oneimportant of “Certain Improvements in fourth to one-fifth of a square inch to the Steam-engine," lately patented by Mr. each horse power, instead of one square Henson. Another of Mr. H.'s improve- inch, as recommended by the most emiments consists in the application of a nent engineers. In the other seventeen governor to the safety-valve of steam cases of the nineteen, the ebullition had engine boilers, by which the safety-valve not been continued in the boilers while is raised when the engine is at rest, and the engines stopped. the danger of explosion from the sudden The greatest number of boilers have stoppage of ebullition in the boiler there- ruptured below the water-line, caused by prevented. The present paper ex.. apparently by some sudden action under plains Mr. H.'s views in this improve. water. The most violent explosions have ment; they are ingenious, shrewd, and generally taken place just ai the instant original, and well deserving of attention. of setting the engines in motion after -ED. M. M.]

standing quiet some time with no steam I find by the Government Report on escaping, and consequently no ebullition. steam-vessel accidents, published in 1839, These explosions have generally been at. that, out of twenty-three explosions, nine tributed to the lowness of the water in the teen occurred whilst the vessels were on boiler, and the exposed parts getting red the instant of starting, or were stationary; hot, whereby, when the water is agitated three whilst steaming; and the time when by the engine being set on, or by the the remaining one took place was not as safety-valve being suddenly opened, or certained. In two instances only was it even by the oscillating of the vessel, a proved that steam was blowing through thin sheet of water has washed over the

ON THE CAUSE OF EXPLOSION IN STEAM-BOILERS, AND THE REMEDY.

227

red-hot parts, causing, as suggested, the throughout a greater space. Therefore, adden formation of such an immense vo as every particle of water requires a much lume of steam, that no safety-valves could higher temperature than 212° before it relieve the boiler in time to save it. But can expand into steam, it appears that if if ebullition had been continued when the heat could be communicated equally to engine stopped, this cause of explosion every particle of water, and the water could not have arisen, as the ebullition kept perfectly still at the same time, the vould most probably have prevented the water would attain a much higher temboiler getting red hot, at least those parts perature than 212° Fahr. before the whole near the water. The water has been of it flashed into steam. This I am aware known to get very low while the engines is not easy to accomplish, on account of were at work, without any accident hap water at rest not being so good a conpening, yet the same boilers have ex ductor of heat as when in motion ; and ploded whilst the engines were stopping, those parts which are hottest, being vith every reason to suppose there was lighter than the other parts, will rise to plenty of water, and the safety-valves not the surface and disturb the stillness. This overloaded. In several instances it has tendency of the most heated parts to rise been proved that a sufficiency of water to the surface causes a number of currents has been in the boilers at the time of the to move in various directions, and these explosions, and the vessels have performed currents appear to assist materially in the in safety regular voyages across seas which formation of steam, by enabling certain required good seaworthy vessels and strong portions of water to concentrate sufficient boilers, yet these boilers have exploded heat in themselves, from the surrounding whilst preparing to start, or on the instant portions, to form steam. of starting from the quays or ports where I have found by experiment that water they have been stopping, and weakness kept very still, and heat communicated and insufficiency of stays has been attri gradually, it did not boil, although conbuted as the cause.

siderably above the boiling point; but Many persons have contended that the upon agitating the water a little, even extreme violence of some explosions is when the fire was removed, a portion of caused by the over-heated parts of the it instantly flashed into steam, driving boilers decomposing the steam and gene some of the water with considerable viorating a highly explosive mixture of gases. lence against the upper side of the vessel, It is true that red-hot iron will decompose and a very brisk ebullition continued for steam, but in doing this the oxygen com a space of about a minute afterwards, bines with the iron, and the hydrogen until the temperature of the water was alone is set free, which is not explosive reduced to the boiling point. This expeby itself. In no instance, I believe, have riment was tried at a low temperature, the two gases been proved to be produced with a close vessel, from which the atunder these circumstances.

mospheric air was excluded. The upper From various incidents I have been led part of the vessel was kept at a low to believe that there may be another temperature (about 60° Fahr.) and the cause of explosion which has hitherto lower part heated very gradually by inescaped observation. I will endeavour to terposing dry sand between the fire and explain it as briefly as possible. It is well the vessel. I have by this means heated known that water boils, under the ordi the water something more than 100°Fahr. nary pressure of the atmosphere, at 212° above the boiling point.

As it is very Fahr., and that it takes about five times as probable that the effect above described long to convert a given quantity of water is produced equally at high temperatures, into steam at 212° as it does to raise the I think its violence is quite sufficient to water from the ordinary temperature to account for some of the phenomena of the boiling point. It follows that this steam-boiler. explosions. “Again, if a steam contains about five times the quan- bottle containing a little cold water, or tity of caloric to its equivalent in water, almost any other liquid, be corked lightly, or, in other words, that the steam contains and then shaken well, there will be five times as much heat as it contained sufficient vapour formed by the agitation when in the state of water at 212°; but of the water, and the escape of the gases the additional heat is not sensible to the contained therein, to blow out the cork. thermometer, because it is expanded But to produce a still greater effect, put

a little water into a deep bottle and cork effects of the slow communication of it up, leaving a small aperture open to caloric to the particles of water. I will the atmosphere, and then boil the water now point out how the conditions necesby means of a spirit-lamp; when the sary for that purpose are fulfilled in the steam has heated the whole of the bottle, generality of steam-boat boilers. The and escapes freely from the aperture, re Hues which contain the fire-grate, and move the bottle from the lamp; and when conduct the heated air through the body the steam has ceased to blow out, and the of water, pass longitudinally

through the ebullition stopped, turn the bottle on one boiler. The greater part of the heat is side, or give it a good shake, when a con absorbed by the water on the top and siderable volume of steam will instantly be sides of these flues, but still a consideragenerated, which will blow out the cork. ble portion is absorbed by the lower This experiment shows the necessity of side. When the engine is at rest, and having a large surface of water for the steam no ebullition going on, that portion of to escape from in a steam-boiler, and the water situated just under the flue, in condanger of allowing the water to remain sequence of being heated on the upper quiet. I will also observe, that with a surface, absorbs the heat very gradually, sufficiency of water in a boiler, and good without causing motion amongst its parsafety valves, not overloaded, there is less ticles, because those portions on the danger with a brisk fire than with a slow upper side nearest the bottom being one, as the former would continue the lighter on account of being hotter than ebullition while the engine was stopping the portions immediately underneath, by generating sufficient steam to force have no tendency to cause those currents open the safety valves, thereby prevent in the water which appear to assist so ing the formation of great quantities of much in causing ebullition. Thus that steam.

portion of water directly under the flue The sudden commencement of ebulli becomes heated very considerably above tion has also a tendency to strain parts of the boiling point, and when any thing a boiler by the contraction of the iron occurs, as the starting of the engine, &c., arising from the cooling effect peculiar to to cause agitation or vibration, a great evaporation at all temperatures. The body of steam is instantly formed, which well-known experiment of taking a ves impinges against the under side of the sel containing water boiling hard from the flue, and the bottom of the boiler. The fire, and resting it upon the hand without water is by this means driven for a mopain, though it cannot be borne for a ment against the top of the boiler, chokmoment after the ebullition has quite ing up the safety-valves, and by the great ceased, is sufficient to prove this fact. The agitation into which it is suddenly thrown, Americans appear to be well aware of the causing every part to give out an addi. danger to their steam-engine boilers of tional quantity of steam, whereby the stopping, without knowing whence the under side of the flue, if not very strong, danger arises; but by disconnecting the will probably be collapsed; and it is a paddle-wheels from the engine, they are fact that in most cases of collapse the enabled to stop the vessel without stop flues have ruptured on the under side. ping the engine, though in this case a The violent force with which the greater fly-wheel is necessary, or the engine part of the water may be thrown against would not work at all. But it is not re the upper surface of the boiler by this quisite to continue the engine at work if means, may account in some measure for a certain quantity of steam be allowed to the singular but well-known phenomenon escape; the effect in the boiler will be of an entire boiler being lifted from its exactly the same as if the engine was at seat, and the great additional volume of work, and water may be very readily steam which is given out by boiling water supplied to the boiler without the assist when violently agitated, may explain the ance of the engine.

fact of its bursting in the air. It is generally believed that explosions From these experiments and investihave taken place when there has been a gations I have been led to form the sufficiency of water in the boilers at the opinion that if the ebullition in a boiler moment of opening the safety valves sud can be constantly kept up, explosion is denly, or of setting the engines in motion. not likely to happen; and to continue the I have already shown what may be the ebullition, therefore, while an engine is

PROGRESS OF FOREIGN SCIENCE.

229 stationary, I have introduced the improve “the regulator,” carries at each end a Dient above described, into the boilers of smaller arm,

called “ an indicator." The steam-engines.

regulator, moving on an axis in the middle of its length, is either horizontal,

vertical, or at 45° of inclination; each PROGRESS OF FOREIGN SCIENCE. indicator turning on its extremity, is per[In continuation from page 203.]

pendicular, or at 45° to the regulator, The Gases evolved in Blast Furnaces. and never takes six positions with referOn the 17th of January last, M. Ebel.

ence to the latter. Recently in some of men read a memoir to the Academy on

the government telegraphs, the regulator his method of employing usefully the

has been fixed horizontally, and the place

of its four positions supplied by a sepagases given off by iron furnaces when in Elast, and on the constitution of these gases.

rate bar, placed above, and moving like The chemical reader is probably aware

the beam of a balance; this upper bar

the French call “ mobile," for which it that a good while ago Ñ. Bunsen, of Marbourg, whose laborious, dangerous,

is not easy to find an English word. and beautiful researches on alkarsin and

M. Vilallougue's telegraph adopts the its compounds, have made his name

same principles of notation as this latter, celebrated, conducted also a long course

but his mechanical arrangement is such of experiments upon the

as gives greater facility in working the evolved in

gases blast furnaces.

machine, greater clearness in hazy weaThe results both of his, and of Ebel.

ther, &c.; and enables the same instrumen's researches, though of considerable

ment to answer as a day and night telechemical interest, do not seem to have

graph, with only the loss of two minutes thrown much additional light upon the

time to change it from one to the other. metallurgy of iron. The value of the

His telegraph tower is square, and economic applications of the combustible painted black externally: On one of its

faces it carries three large dials, like gases given off, as proposed by the latter,

clock dials without figures, made of wood, has yet to be proved.

or sheet iron, and moveable in a vertical Electro-chemical properties of Gold,

plane round their respective centres. M. Becquerel has commenced reading Each of these is about 9 feet in diameter. to the Academy of Sciences of Paris, the The two lower ones are placed side by first of a series of memoirs on “The

side on the same level; the third is placed Electro-chemical properties of the simple centrally and above them. bodies, and on their applications in the Below the two lower dials a bar of arts." The first memoir is On Gold-it

wood, painted white, is placed, behind is of great length, and treats minutely of which is an aperture of the same size several of the most important operations into the interior of the tower. This bar in the metallurgy of this metal, methods

is horizontal, and represents the fixed of gilding, &c. When this series of regulator of the present system. Each of memoirs shall be complete, a translation the two lower dials has got a radius published in a cheap form would be a

wide. The upper dial has got a diameter, most useful addition to our scientific

painted white, upon it, of two decimetres literature.

painted white, upon it. Means are proThe new French Telegraph vided inside the tower for turning these of M. Vilallougue.

dials on their centres in any way required, This is the age of telegraphs and tele and by the respective positions of the graphing: We have electric telegraphs diameter, with the two radii and the regufor regaining our top-coats when left lating bar, the signals are conveyed. behind on the railways; and semaphores, The opposite side of the tower carries to tell us the cream of the news as it a precisely similar set of dials, &c., whose comes across the Atlantic by steam; and axes are the same (i. e. on the same we get the first of our news from India, shafts) as the former, so that the signals whether good or bad, across France by are made on two faces at once; thus the telegraph.

watchman at the former, or last station, The existing telegraphs in France con always sees what signals are making by sist of three arms, moveable in the same the next telegraph to him to that beyond, vertical plane ; the principal arm, called by which he knows if his own signals

have been correctly seen and observed.

Photography. So much for the day telegraph, which, in M. Nothomb has addressed a note to experiments made at Perpignan, was dis the Academy of Sciences, stating that he tinctly seen with telescopes magnifying has found it advantageous to substitute from thirty to forty times, at 8000 metres proto-chloride of mercury in place of distance, which is about the mean tele- running mercury, (quicksilver,) as prographic distance. To convert this into posed by Daguerre. The proto-chloride a night telegraph, the white bars on the is the calomel of the Pharmacopoeia. several dials, and the regulator bar, are Dilatation of Elastic Fluids. movable, and in their place, when re

Most persons are aware, who follow moved, is formed a band of a built lens,

the course of science, that the coefficient that is to say, a strip cut out of one of of dilatation of elastic fluids, which until Fresnel's lenses, (the polyzonal lenses of a comparatively recent period had been Brewster,) by two planes, parallel and

assumed the same for every gas, and such equidistant, from a diameter. The breadth that the dilatation was to part of the of this slice of lens being equal to that of volume for each degree of Fahrenheit's the white strip or band before spoken of, thermometer, has more recently been the interior of the tower is strongly illu submitted to new researches by Regminated by lamps like a lighthouse, or nault, Despretz, and others. M. Magnus single attached lamps are placed in the is the latest experimenter in this field, focus of each band of lens, and the whole

and has not yet concluded his researches, is now in a condition to work as a night which are of great value : he has, howtelegraph.

ever, already ascertained that the coefThe acknowledged difficulties of night ficient of dilatation is not precisely the telegraphs are thus much reduced, if not

same for all gases, and that the difference got rid of; and the whole instrument is does not arise from the easy condensibility worked free from the inconvenience of

of some, such as sulphurous acid, into weather, &c.

liquids. It has also been found advantageous to

Nicotin, substitute for the band of lens two simple The vegetable alkali of tobacco has glazed apertures at each end of the dia

been carefully prepared and analyzed, meter in the upper dial, and at the ex with experiments of controul by M. Bartremities of the radii of the lower ones, ral: it is a colourless anhydrous fluid, and of the regulator. There appear to which does not freeze at 10° cent. ; it has be several pot inconsiderable advantages a burning taste, and is volatile at 250° secured by this arrangement, which has cent., and is a violent poison ; a single been approved of by the Academy of drop placed on the tongue of a middleSciences, after having been reported on

sized dog poisoned him in three minutes. by a commission of its members.

It reacts alkaline, Its composition is New Method of Purifying Gas. CH Az. M. Mallet has had in operation for some time, at the gas-works at St. Quen

Coal in France. tin, a new method of purifying gas,

The coal formation of the basin of the which was described to the Academy of Soane and Loire has lately been described Sciences in August last. The results are in a memoir by M. Burat, which is of said to give a gas of the highest purity, considerable interest. The coal in this free from naphthaline, which is what formation is different from any yet known, makes the chief part of the smoke that as to its mode of deposition: it is not blackens our ceilings, in our own gas regularly in beds, but rather in fast from coal; and equally free from various masses, which surpass in thickness or ammoniacal compounds, which give much depth any thing previously known, but are of the detestable smell to coal gas when of no great horizontal extent. In some it escapes. The gas at St. Quentin, places the coal is confounded with the though candidly admitted by the inventor other matters of the formation. of this process of purification not to be Artesian Well of Grenelle. absolutely without smell, has yet very The public excitement in Paris, as to little, and that scarcely, if at all, offensive. the formidable consequences which will It would be very desirable if our own Gas result to the city from the well at Gre. Companies would adopt something of this nelle, unless speedily filled up, and which sort.

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