heat which is thus transferred from the burning fuel to the boiler, induced by the law of equal diffusion, the gases emanating therefrom being of a much higher temperature than the boiler, is transmitted from the boiler to the water within, in obedience to the primary law; the temperature of the boiler being higher than that of the water, and the heat thus transferred to the water, ascends to its upper service in obedience to the secondary law, the law of recession; and thus the first portion of heat imparted to the water, although received at its lowest surface, ascends to the upper, and the temperature of the upper surface becomes great. er than the lower. The decomposition of fuel and air, and the impartation of the resulting liberated heat continuing, the temperature of the upper surface of the water soon amounts to 212 degrees, when the formation of steam commences: and the safety and eduction valves of the boiler being closed, the steam which is generated on the upper surface of the water evolates, and the generation and evolation continuing, the space above the surface of the water would soon be filled with steam, was it not already filled with air; but as such air is elastic, the volume is compressed into a smaller space by the expulsion of a portion of its constitutent heat through the metal composing the top of the boiler, and the boiler being so charged with heated water, steam, and condensed air, we will suppose that either the safety or the eduction valve is opened and the air rushes out, leaving the boiler charged with water and steam only, the valve being again shut. We will next suppose that the temperature of the water from the upper to the lower surface, has attained to about 212 degrees or boiling heat, and the boiler being completely full of water and steam, the question is, can any more heat be imparted to either water or steam? we think not, because the receptive capacity of either water or steam for heat is not to a greater amount than about 212 degrees, and because no addition can be made to a plenum. But it is said that steam is compressible and expansive, and that in these two properties consists the accumulation and the exercise of the motive power with which it is endued, and that the amount of the power generated is proportionate to the extent of the compression; and hence we hear of the generation of steam, and its compression within the boiler to such an extent as to cause its pressure upon the internal surface of the boiler to be equal to the pressure of so many atmospheres; but we are decidedly of opinion that steam is neither compressible nor expansive, (unless in a vaccuum) and although a volume of steam may be

evolved from a boiler, and occupy a tenfold space subsquent to its liberation than it possibly could in the boiler, yet that is by no means a confirmation to us that steam is either compressible or expansive; and we deem that the proofs offered in favour of the doctrine of its compressibility or expansibility are diametrically opposed to the possibility of the occurrence of either, and to all the well known results, which ensue from the impartation and abstraction of heat. If we ask what is the effect of the impartation of heat to water, we are told to cause its expansion or increase in bulk, until its diminution commences by the generation of steam, and its evolation from the surface of the water; and we are told that if the impartation is continued, that the boiler will eventually be filled with water and steam, and up to the point of repletion expansion has been the result of the impartation of heat; and then it is endeavoured to convince us, that by a yet further impartation of heat, that a compression or diminution of the steam which first occupied the whole space within the boiler above the water is effected by the production of more steam by heat subsequently imparted; but to suppose that heat can cause both the expansion and the contraction of a fluid appears to us to be impossible, and not supported or countenanced by any analogous proofs; for if we examine the resulting effects of the condensation of atmospheric air, we find that heat is evolved and not imparted in the process, and that it is only by the expulsion of a portion of the constituent heat, that the ponderable atoms can be brought closer together, and thereby cause its volume to be reduced in bulk. will then perhaps be asked, to what do we attribute the increase of power furnished to steam by the impartation of heat in the ratio of the amount imparted, and to the production of a greater amount of steam than the space within the boiler above the water could possibly contain without compression, or a diminution of its bulk, and its subsequent expansion or increase of its bulk, which it experiences on its liberation from the boiler, and also the cause of the bursting of the ber, in case the steam is not liberated r.evious to the generation of such an amount, and its compression to such an extent, as to cause an internal pressure upon the boiler which it is unable to bear? To which our reply is, that we conceive that the formation of more stean than the space above the water within the boiler will contain is impossible pro ious to its exit; that the compression and expansion is apparent and not real; that an accumulation of heat in the metal of the boiler and its appendages, and in the surrounding brick-work

It

and atmosphere, occurs in consequence of the inability of either water or steam to receive more heat; that the heat accumulated in the boiler and the surrounding media, presses upon the water and steam within the boiler in virtue of the law of equal diffusion, with a power and force proportionate to the extent of endowment conferred upon it by such law, and the difference in the amount of the heat accumulated and communicable, and the amount possessed by the water and steam within the boiler; that the pressure upon the internal surface of the boiler is a reverberating, reflective or recoiling pressure, resulting from the pressure of heat upon the water and steam, in its endeavour to force its admission into the water and steam in obedience to the law of equal diffusion, and not an expansive force exerted by an increase in the bulk of either water or steam, beyond their receptive capacities for heat; that between the impulsive power of heat, which may be compared to a power operating upon a lever, and the resisting power of the water and steam, which may be compared to a weight to be raised by such imaginary lever, the sustaining boiler may be compared to the fulcrum of such lever, and which if not of sufficient strength to sustain the force of pressure exerted upon it by the impulsive and resisting powers, its disruption necessarily ensues. We conceive also that the amount of the motive power of steam which is generated within the boiler, previous to its bursting, or its exit by the safety or eduction valves, is no more than the difference between its specific gravity and that of the surrounding atmosphere-a difference so slight as will be found very far inferior to account for the rapidity and force of its exit; but we atribute all the acquired force to the formation of an additional quantity of steam subsequent to the bursting of the boiler, or the opening of the safety or eduction valves, by the very rapid transition of the accumulated heat in the boiler and surrounding media to the water within the boiler, as soon as the first amount generated has made its exit, and that the apparent expansion of a large amount of steam compressed into a small space previous to its exit from the boiler, is but the rapid formation of a large additional quantity, subsequent to the liberation of the first amount created.

We admit of the expansibility of steam within the cylinder of the steam engine, resulting from the creation of a vacuum therein by the ascent or descent of the piston, and the consequent absence of atmospheric air, which if present would keep the constituent atoms of steam within their ordinary limits; but such expansion is not the effect of an

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innate power impelling its constituent atoms to occupy a greater space, but of the removal or absence of a restraining power which under customary circumstances, circumscribes the limits of the space which steam can occupy; and hence such expansion is unproductive of impulsive power.

If then the theorem which we have advanced is correct, it appears to us that the liability to burst, to which a steam boiler is subject, is due to several causes. We conceive that no created substance is able to resist the diffusive power of heat, and that such diffusive power is proportionate in amount to the difference between the temperature of the impartive and the receptive medium. That the accumulation of heat in the metal of the boiler beyond the receptive capacity of the water and steam within the boiler, causes a recoiling force or pressure upon the surface of the metal of the boiler, proportionate in power to the amount of heat accumulated. That the heat which is thus imparted to the metal composing the boiler and retained by it, separates the ponderable atoms of which it is composed further from each other, and thereby diminishes the force of attraction of cohesion and aggregation which holds those atoms united, to an extent proportionate to the amount of heat imparted and retained, and the consequent separation to which its ponderable atoms are subject; and that as what is termed the strength or tenuity of the metal is dependant upon the force of the power of attraction of cohesion and aggregation by which those ponderable atoms are held united together, so in proportion to the amount of heat imparted and retained must be the distance of removal of those ponderable atoms from each other, and the consequent diminution of the force and power of the attraction of cohesion and aggregation subsisting between those atoms, and the resulting diminution in the strength or tenuity of the metal.

In the generation of steam as a motive power, the purport is not merely to render a portion of the water of less specific gravity than the atmosphere, by the impartation of as much heat as will separate its ponderable atoms so far apart, as to occupy such a space as will render the whole of less weight than the bulk of atmospheric air which they together have displaced, and thereby enable the new compound called steam, merely to evolate from the surface of the water which supplied the ponderable atoms as a principle, and the imponderable as an agent; but the purport, in addition, is to generate an impulsive as well as an evolating power, and to invest steam with it, in order that it may accomplish the several purposes for which it is created. If steam is generated

to an amount just sufficient to occupy the space between the water within the boiler and its upper portion, and the safety and eduction valves are closed, and the temperature of the water and steam within the boiler, and the metal composing the boiler, are at 212 degrees of heat, and no more heat is imparted, and the safety or eduction valves are then opened, it will be found that the steam which has been generated will evolate from the boiler with as much force as will be induced by the amount of the difference in the specific gravity of such steam, and the superincumbent atmosphere; but such force will not furnish a motive power adequate to the need of any mechanical operation; and if the safety or eduction valves were allowed to continue open, and the impartation of heat was continued, so as to generate steam with a rapidity no greater than such steam could be evolved from the valve without impediment or restraint, we might cause the whole of the water in the boiler to evaporate, without furnishing a motive power to an adequate amount, and during the process up to its termination, we should find that the temperature of the water, steam, or boiler, never exceeded about 212 degrees; but if we generate steam faster than it can pass such safety or eduction valves free from restraint, we still find that the water and steam continue at the same temperature, but that in the same given period of time, a much larger amount of steam passes by such valve, and consequently with a much greater degree of force than it had previously passed, and thereby an available motive power is furnished. Such being the case, we therefore conclude, that in order to invest steam with a motive power, it must be generated faster in the steam compartment of the boiler, than it can pass free and unrestricted by the safety or eduction valves; that the smaller the orifices are which such valves cover, the greater will be the force with which the steam will pass through them; and the force with which the steam generated will pass, will be proportionate to the difference in the amount created, which would pass in virtue of its lesser specific gravity than the atmosphere, and which will be able to pass impulsively. And what is the impulsive power? The heat imparted from the fuel to the boiler, and from the boiler to the water. But it is said, that neither water nor steam can receive any more heat after it has attained to the thermometic temperature of about 212 degrees; and if neither can receive any more heat, how then can the heat imparted to the boiler, and which cannot be received by the water within the boiler, or the steam already generated, impart an impulsive power to such steam as issues from

the orifice of the safety or eduction valves? The reply to which is, that if heat is imparted to the boiler faster than the water can receive it, the surplus quantity will be accumulated and retained by the metal com posing the boiler, and such heat will press upon the steam already generated, with a force proportionate to the amount accumulated, multiplied by the power of equal diffusion to which such heat is subject; and should the amount thus accumulated so far diminish the tenuity of the metal, and increase the recoiling pressure upon the internal surface of the boiler as to exceed its ability to bear it, its disruption must then necessarily occur.

We have already observed, that it is usual to charge a steam boiler in the first instance with water to a definite height, and that it is usual to endeavour to regulate the supply of water to the boiler during the process of the generation of steam to an amount, and with a rapidity proportionate to its consumption in such creation, so as that its depth shall not exceed or fall short of such point which is called the water line; and that the height of the furnace flue around the sides of the boiler, is but a little short of such water line, and that the purport of such arrangement is to endeavour to cause the impartation of as much heat as is furnished by the fuel to the boiler as can possibly be effected, and to impart no more than the water within can receive; and hence it necessarily follows that if the supply of water to the boiler is not sufficient to cover any portion of that part which is exposed to the action of the fire within the flue, and that the accumulation of heat will occur in the metal which is thus exposed, and the impartation being above the water, such heat will in obedience to the laws of equal diffusion and recession, rapidly ascend and become diffused throughout the entire surface of the boiler, and gradually accumulate to the amount of disruption of the boiler, provided the impartation of heat is continued, and its subsequent abstraction is not effected. And it should be well understood, that a subsequent abstraction may become a dangerous remedy if injudiciously administered, for if instead of diminishing the supply of heat, and allowing the escape of the surplus heat accumulated in the boiler by gradual radiation, a large amount of water is injected into the boiler to raise the supply to the water line, and such water is cold and too rapidly injected, the probable result will be the disruption of the boiler, by the too rapid increase of the amount of difference between the temperature of the boiler and the water, thereby increasing the amount of the power of equal diffusion to which the heat in the boiler is subject, causing a con

sequent greater recoiling pressure upon the boiler.

It is the opinion of some, that one of the causes of the bursting of steam boilers, is the decomposition of the water within by its primary conversion into steam, and a subsequent decomposition of such steam, a combination of the oxygen of the water with the metal composing the boiler, leaving its hydrogen subject to ignition by the highly heated metal, and that the disruption of the boiler is to be attributed to the explosive decomposition of such hydrogen; but without questioning the possibility of such an occurrence in a wrought iron boiler, we very much doubt the probability of it.

The following summary list of causes or means by which the disruption of a steam boiler may be effected, we conceive may be useful.

To charge a boiler full with cold water; to load the safety valve with a weight greater than the cohesive strength or tenuity of the metal of which such boiler is composed; to shut the eduction valve, and then to impart heat to such water by medium of the metal of the boiler, to a sufficient amount to cause disruption, and probably to a much less amount than is sufficient to raise the temperature of such water to 212 degrees.

To charge a boiler to the usual water line, load the safety valve as before, shut the eduction valve, and impart heat, and disruption will probably occur, before the lower surface of the water in the boiler has attained to the temperature of 212 degrees.

To properly charge the boiler to the water line, and continue the supply to such point, neither above nor below, during the whole process of the generation of steam, and impart heat to the boiler more rapidly than the water within can receive it, and to an amount in accumulation in the metal composing the boiler sufficient to diminish its tenuity to a disruptive extent, in conjunction with the recoiling pressure of the heat accumulated upon the internal surface of the boiler; the safety valve being at the same time properly loaded, and the eduction valve opened and shut at an unrestricted speed of the engine.

To properly charge the boile. to the water line, to reduce the charge below the water line during the process of the generation of steam by insufficient injection, and thereby increase the area of the steam compartment; to impart heat to the boiler with a rapidity, and to an amount perfectly safe and proper, with the boiler charged and kept charged to the water line, but owing to the increased area of the steam compartment, and the diminished area of the water compartment, the accumulation of heat in the boiler beyond the receptive capacity for heat of the

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water and steam may be such as to cause the disruption of the boiler. although the safety valve may be properly loaded and the eduction valve opened sufficiently frequent.

To overload the safety valve; the accidental adherence of the safety valve; the irregular or inefficient opening of the eduction valve; the irregular or insufficient reception of steam by the cylinder of the engine; an accidental or designed overloading of the engine, or an endeavour to cause it to perform more work than it is able to accomplish, thereby causing a diminished consumption of steam and a consequent reactive pressure of the steam upon the boiler; an accretion of calcareous earth by deposition from the water to the internal surface of the boiler, the consequent additional impediment presented to the rapid transition of heat from the boiler to the water and the resulting accumulation of heat in the metal and accreting substance; the liability of such calcareous coating being separated in portions from the surface of the boiler by the effect termed blistering, and the transmission of heat from such part of the boiler to the water being nearly suspended, an accumulation of heat in the metal may occur to the extent of its disruption. These, and most probably other causes which do not at present offer themselves to our memory, may severally or conjunctively effect the bursting of steam boilers.

We have stated that the capacity of both water and steam for thermometric heat does not exceed about 212 degrees, and it may be here necessary to explain, that although the thermometric temperature of steam does not exceed that of water, yet that its constituent amount of heat far exceeds that of water, and that in the conversion of water into steam, it is not only necessary first to raise the temperature of the water to about 212 degrees of thermometric heat, but to impart a large additional quantity of heat to such water to convert it into steam, and that the cause which prevents such additional quantity from passing by transition to the mercury of the thermometer, is because such heat becomes latent in virtue of its constituency, and is therefore not subject to the law of equal diffusion to any body which may have attained to its own thermometric temperature. In the generation of steam for the purpose of imparting heat to the other bodies or substances, should they be situated at some distance from the steam boiler, it is necessary that such steam should be furnished with a motive power to enable it to reach its destination, and it is necessary that the conveying pipes should be covered with some non-conducting heat material, in order to prevent an unnecessary diminution

of that motive power, and a loss of valuable heat by abstraction in its passage, and it will be found that an abstraction of the constituent heat of such steam by any body or substance will be accomplished, while the abstracting substance is of a lower thermometric temperature than about 212 degrees. pp. 327-336.

NOTES AND NOTICES.

Origin of Railroads.-The German newspapers on mentioning the approaching completion of the railroad from Brunswick to the Harz, take occasion to remark, that the Harz was the " cradle of railroads" altogether. It was, they say, to miners from that district, whom Queen Elizabeth imported into England for the purpose of improving the English process of mining, that the first railroad ever seen in England owed its origin. So early as 1676, they remark, coals were conveyed from the nines in the vicinity of Newcastle-upon-Tyne to the neighbouring river by means of an imperfect railroad, which enabled as much work to be done, with the assist'; ance of one horse, as formerly with that of fourand a similar contrivance was, they assert, long before in use in Germany. If it be true that the invention was practised in Germany previous to its application at Newcastle, it is not very easy to see why the phrase, "so early as 1676," should be made use of; and, if it is to miners invited into England by Queen Elizabeth that its introduction is due, it is rather singular that it should be "so late as 1676" before it was introduced, no less than seventy years after the death of that illustrious princess. The whole story bears about it marks of incorrectness, if not of fabrication.

Steam-carriages on common roads.-Mr. Hancock and Sir James Anderson are, it appears, to have a foreign rival. On the 14th of October, M. Dietz performed a journey on the high road, from Brussels to Ghent, in a locomotive steam-carriage, to which several others were attached. The road was crowded with spectators; but, to the amazement of all, M. Dietz succeeded in guiding his train not only without any accident or inconvenience to the public, but without ever being compelled to stop his movements or to abate his speed. A performance which must, indeed, have required a remarkable degree of dexterity anywhere, and which, we think, Mr. Hancock might safely challenge his foreign opponent to repeat on his scenes of action, the City-road and Cheapside. There seems to be an unusual degree of activity prevalent just now in this highly interesting and important branch of inventions, and we believe the time cannot now be far distant, when it must either "come to something," or come to a stand-stlll. M. Dietz, however, does not confine his exertions to steamcarriages only. It is stated in the foreign journals that the King of the Netherlands has granted him a privilege, and made pecuniary advances for the execution of another plan of his-a patent mechanical carriage without steam, in which two horses are to draw six carriages, containing eighty passengers, on common roads. Great things are to be done" if the scheme succeeds." We suppose so.

Railway Masks.-Half masks of gauze are now sold at Leipzig, for the protection of the eyes during railway journies. The price is two groschen each.

Chelsea Water-works.-At a recent meeting of the Directors of the Chelsea water-works, Mr. Lyon the Secretary laid before the Board a statement of the progress of the new filtering receivers which are now nearly completed. They occupy a space of 48,000 square yards superfices. The filtering bottoms consist of 12,000 cubic yards of pebble, siliceous gravel, and shelly sand; and they have been constructed at an expense of 57,000l. The pipes are laid eight feet below the surface of this bottom, through which the water is filtered and cleansed before it passes into the wells from which the mains are supplied. It was further stated, that the brewers in the district consider the water as good for their purposes as that derived from the Artesian springs, and the custom of the Company had been thereby vastly increased since the adoption of the new filters. In the hearing of the reporter, however, it was remarked by a proprietor that the project of Artesian springs would eompel the other water companies of the metropolis to follow the example of the Chelsea Company, and to adopt this cheaper and readier means of supplying filtered water without the intervention of Mr. George Robins.

Mousseline-de-laine Manufacture.-This appears to be a new species of manufacture, and as such is likely to become very valuable. The Glasgow Constitutional says:-The Mousseline-de-laines were first introduced into this country about three years ago, in a fabric composed wholly of wool, within the reach only of the wealthier classes. To meet, however, the pretensions of all ranks in society, a mixed fabric constituting of cotton and wool, was substituted, coarser wools being employed; and the trade having got into a number of hands, the Mousseline-de-laine may now adorn the person of any one who can command the price of a common chintz. Formerly immense quantities were imported from France, on payment of a heavy duty; and when first introduced sold at most extravagant prices, but now the foreign goods have been met with such active opposition from the British manufacturer, that they are nearly driven out of the market. France has always had the reputation of producing the finest printed goods in the world; and had our Gallic neighbours not met with such powerful competitors in the British, they might, for a long time, and for the higher description of goods, have commanded a complete monopoly of the British market. At this moment the number of hands engaged in this trade is enormous. Besides those who are occupied at the printing tables, a great proportion, nearly one-half, of the hand-loom weavers in Scotland are in full operation in manufacturing the cloth. In almost all the small manufacturing villages in the west there is scarcely a loom idle; and we are pretty safe in saying that there is not a respectable weaver who will find any difficulty in obtaining employment from the Mousseline-de-laine manufacturers. This trade has given a mighty impulse to the wool trade, but at the same time it has considerably weakened the hands of the cottonspinners, who are complaining of the small demand for particular sorts of their yarns. Besides other important attribut s, they possess one intrinsic advantage-they not at all ignite on coming in contact with .ame, like muslins or calicoes.