Had we the means of observing what is really taking place in the interior of furnaces and flues-of ascertaining what kinds of gas are generated during the successive stages of the process — to what extent they enter into combustion : whether visible or invisible smoke be generated-to what extent, at what times, and from what causes: were we enabled to observe the effect of admitting or excluding air—and above all, of ascertaining the varying degrees of heat produced during these several stages and processes, we would then be in a position to appreciate merit or detect fallacy; and thus decide between truth and error. Now the obtaining correct information on all these points is strictly within our reach.

Again, as to the evaporative power of any particular kind of fuel; with such means of inspection, positive results would be obtained, whereas we are at present dependent on the care, judgment, or prejudices—too often the neglect or evil intentions-of a mere fireman, since much of the result of any trial is absolutely under his control, (as will be shown hereafter,) in the absence of the means of that personal inspection and observation, which would have enabled the proprietor to detect the causes of apparent success on the one hand, or apparent failure on the other. Under the conviction of the value and even necessity of being enabled to form a correct opinion in such cases, I propose showing how the proprietors of works may, with a minimum of trouble and care, be qualified to judge for themselves, and correct the misstatements of interested parties, who would palm upon them some ingenious, but insufficient scheme.

I will now describe the various changes and effects produced in a furnace and its flues from the throwing on of a fresh charge of coal until it is exhausted, and another charge be required; of the correctness of which all can form an opinion.

Let the annexed engraving represent a cylindrical boiler 15 feet long, (the length of that from which I have drawn the following facts,) set over a furnace furnished with the means of admitting air in the proper manner, or of shutting it off at will, for the purpose of noting the varying results. To enable the operator to observe all that is going on in the interior, five glazed spy-holes, or windows,

are provided, as shown at S 1, 2, 3, 4, and 5. By means of the centre one, S 1, placed exactly opposite to, and in the line of the furnace, a distinct view is obtained of what takes place behind the bridge, and even in the furnace itself. This is the most important spot for observation. By S 2 and 3 a view is obtained quite through the left-hand flue; and by S 4 and 5 through that at the right hand. The being thus enabled to see, not only into, but through the flues, is of the greatest importance, as will be shown hereafter.

By these means we are qualified to judge of all matters depending on sight; as, for instance, the length, quantity, and colour of the flame-the alternations in the production of flame or smokethe particular time and circumstances under which such changes take place, and so on; and when we consider how accurate a test is colour-indeed, how often it is the only test, as to the nature of the gas in combustion, and hence the quantity of air required or of heat produced-the value of this visible test will be duly appreciated. Indeed, without the means of knowing what colour the flame assumes, the chemist will inform us it is frequently impossible to decide what species of gas is coming over-at what rate, and in what proportions, they succeed each other-and to what extent they are inflamed. Now this succession of consecutive changes, and their relative effects, forms one of the most instructive and influential objects of inquiry in estimating the operations of the furnace.

So far as ocular demonstration is required, we have thus ample means of detecting errors and drawing correct inferences. As, however, it is absolutely necessary that we should be enabled not only to see, but feel, additional means of information must be supplied. For instance, it is essential we should know what influence the several changes and processes going on in the furnace may exercise as to temperature, and all that belongs to heating and cooling. On these points, the required information may be obtained, approximatively, if not absolutely, by means of thermometers, ranged in the most suitable places, as shown in the annexed engraving, at T 1, 2, 3, 4, and 5. These thermometers are attached to copper bars, as will hereafter be described; the bars being thrust into the flues at

ing one. This is caused by the evaporation of the water or moisture, which is more or less contained in all coal. The presence of this moisture, with its cooling effect, is not, however, to be considered as an evil unaccompanied by a commensurate good. This will be explained as we proceed. After exhibiting a diminished temperature for some minutes, the thermometers begin to rise, as the coal gas (carburetted hydrogen) then evolving from the coal enters into combustion. The colour of the flame, and the distance to which it will extend, will now begin to indicate the nature and quantity of gas generated, and the degree of perfection in which the process of combustion will be effected; while this latter, in its turn, will be dependent on the degree and rate of diffusion which takes place between the atoms of the gas and those of the air; the whole, in fact, depending not so much on the quantity of air introduced, as on the mode of its introduction; and this is the point which practical "smoke burners overlook, but which is beside our present question. I am here, however, presuming that the introduction and diffusion of the air with the gas, is managed in the most efficient manner behind the bridge.

Accordingly, as the air is introduced, properly or improperly, we find the colour of the flame will now become an index of the temperature in the flues; and, in this respect, we shall have under command all the changes and appearances which the Argand gas-burner or oil lamp exhibits; from the extreme of a dark, murky red, with a reduced temperature, up to a clear, brilliant white, with an intense heat; these varied effects being produced by the action of the airvalve, in the same manner, and with equal rapidity, as in the lamp, when we check the admission of air by the centre orifice. If, however, due means be not provided by which these changes of colour and intensity can be seen and compared, how can we venture, while thus literally in the dark, to pronounce on the causes of such changes? As well might we suppose that the Argand burner or lamp could have been perfected, if the experimenters had been prevented seeing and comparing the effects produced, and tracing each to its proper cause. On this head we may also be assured, that as colour is closely allied to intensity, in the nature of flame, much of what is said on

this subject is equally applicable to the combustion of coal gas in the furnace as in the lamp. As the combustion proceeds, the length of the flame will be in the proportion to the quantity of gas generated. This, however, is much more equable than might be supposed; and, to a great extent, is governed by the mode of feeding and the dimensions of the flues.

An important question here arises, respecting the quantity of air admitted at the beginning, middle, and end of the process, from the throwing on a fresh charge, to the time when another will be required. Much has been said on this subject, and many objections raised against the absence of a regulating valve, by which the quantity of air admitted may be in proportion to the quantity of gas evolved. This branch of the subject is a highly important one, and can only be determined when we have some more correct data before us; I will not, therefore, enter on it at present, the question being, in fact, one of expediency, and a balance between the evils of a manual or mechanical adjustment on the one hand, and the inconveniences of the supply being occasionally plus or minus the exact quantity required. Objections, however, against the giving something like system to the admission of air, because it may not be complete, and in perfect harmony with the supposed supply and demand, come with a bad grace from those who have not only overlooked the total absence of all regulation and control as to the admission of air in ordinary furnaces, but advocate-what is still more opposed to chemistry and nature-the compelling the supply of air, both to the gaseous and solid portions of the fuel, to enter by one and the same channel, namely, the ash-pit and bars; by which any adjustment of the required equivalents is rendered absolutely impracticable. And if a regulating principle be necessary, when both the mechanical and chemical impediments, arising out of a single orifice of admission, are removed, à fortiori, it will be more so when the whole supply is confined to the ash-pit alone, with its ever-varying obstructions and facilities, arising out of the states of the furnace, and the fluctuating quantity of fuel on it. Indeed, this new-born zeal for a controlling and regulating influence, seems strange in the

mouths of those who advocate the prevailing system; the prominent and admitted feature of which is, that exactly when the largest quantity of gas is evolved from a fresh charge of coal, the smallest quantity of air is enabled to enter through the bars, by reason of the obstruction which such charge creates.

On this ground, then, I might be excused for throwing the onus on them of providing the suitable means of adjustment. When, however, I come to treat of the two supplies of air, I shall be able to show, practically, how they aid each other, in going far towards accomplishing all that perhaps may be desirable. But

to return.

As the operations of our furnace proceed, the temperatures indicated by the several thermometers will be in the ratio of the heat conveyed by the currents of gaseous products in the flues, at their several stations, and the quantities abstracted and absorbed by the boiler-plate surface, within their respective divisions. Much new and valuable information will be obtained by observing these proportions, and the periods of their relative changes.

If, from the construction of the flues, or other circumstances, which we cannot now stop to examine, the surfaces be not equal to the absorption of the heat generated in the furnace, the excess, (which is an absolute and pro tanto loss,) will be indicated by the thermometer No. 5. And here we have a new and important field for observation, and one which has hitherto been too much neglected. In fact, the variations of internal temperature which the thermometers exhibit under different modes of firing, different kinds of fuel, different modes of managing the same fuel, different states of the atmosphere, and, above all, different modes of admitting or excluding the air, show at once how little reliance can be placed on any calculation of results, unless the quantity of heat thus passing away, and irretrievably lost, be taken into the account; this amount of waste or surplus treat being, in fact, an important element in the inquiry.

In the elaborate report of Dr. Schafaeut, on Player's boiler, we see how much he felt embarrassed by this question, and the difficulty of estimating its amount and calorific value, ranging as it

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did from 230° to 600°, and of course not knowing how much it exceeded that point, from the want of a correct pyrometer. In many of the reports on boilers by Mr. Parkes, we find him embarrassed by the same difficulty-conscious of the heating power he was losing, yet unable to bring it to account. In the experiments by Dr. Fyfe on the evaporative power of coal, the temperature of the escaping gases, or the quantity which passed away in the form of smoke, were wholly neglected. Yet we find him making his calculations exclusively on the other elements of the inquiry, and on these manifestly insufficient data estimating the supposed relative values of anthracite and bituminous coal! Such, indeed, was the difficulty of estimating the heating value of the gaseous products escaping by the chimney, that the learned Doctor thought it safest to throw them fairly overboard, and confine his comparative results to the mere quantity of "fixed carbon, or coke," which each contained. Yet we find, by Mr. Faber's results, that one of those gases alone, the carbonic oxide, (a gas which in ordinary furnaces, to a great extent, passes away unconsumed and invisible,) under proper management, and by a judicious introduction of air, in the very way I have suggested, by small jets, was equal to the production of an intensity of heat suffi

cient for the manufacture of iron.

Of the true calorific value of the escaping heat, under its various modifications, it is difficult to form an estimate, in the absence of a pyrometer of easy application; but a still greater difficulty presents itself as to the mode of turning this waste heat to the purposes of evaporation, when found to be in excess. On this head I hope to be able to suggest a practical remedy, and to this point I am directing particular attention.

It is curious and instructive to note how the eye, where proper means of observation are afforded, sets us right, by explaining and correcting many of the otherwise anomalous changes of temperature which the thermometers, in their respective situations, indicate, and vice versa. The thermometers, under certain circumstances, rising when, according to our received notions, they should have fallen, prove that some indicator of this kind was wanting; while the eye, that

infallible corrector of theoretic fallacies, proves how erroneous have been our notions, in many points connected with the source, and existence, and character, of visible flame. During the entire process I have been describing, from the beginning to the end of the change, we perceive no indications of any sudden action or effect: all proceeds with a regular ascending and descending progression, the whole being a succession of well-defined changes, completely under control, and exhibiting a beautiful and instructive series of causes and effects. Without those aids, however, which the eye and the thermometer afford, much would have been unintelligible, often apparently capricious, and even contradictory of what might have been predicated under the circumstances. It is by such means we are enabled to penetrate, as it were, the secret operations of nature, and correct our own erroneous notions and calculations. It is thus we may be said to be experimenting on the great scale, with all the accuracy and certainty of laboratory practice. By means of the eye, the chemist is enabled to detect the presence of what otherwise he could not have expected; and by that of the thermometers, to trace effects to causes, which, without such aid, would have been impossible.

In my next I will pursue the subject farther, and describe the several gases in the order in which they are developed, and enter into combustion, with the visible and thermometric changes which follow, and the relation they bear to each other.

I here take the opportunity of observing, that as my only object is to improve our practice by commemorating the facts which have come under my own observation, and showing their connexion with scientific details, and chemical analysis, according to the best authorities, I am quite indifferent to the charges with which I have been assailed, of broaching new theories, or new views of combustion. I have no such pretension, and aim at nothing but practical improvement, and not in the character of an amateur, but strictly within the province of my duties, and in furtherance of the interests of the company in which I am interested. I have sufficiently, in the Preface to my Treatise on Combustion, shown how in self-defence I had been driven to the necessity

of examining for myself, and endeavouring to find a way out of that dangerous uncertainty, in which all steam-consumers, steam-shipping companies in particular, are involved, in all that concerns the expenditure of fuel, and the construc tion of furnaces and boilers. Repetition, therefore, would here be misplaced, although the facts are interesting in a public point of view, as the subject is one of deep interest to the community.

One of my objects in bringing the practical details of the subject thus before the public, through the appropriate columns of the Mechanics' Magazine, was in the hope of meeting useful comment, and exciting others to labour in the same field of practical improvement. I find it therefore inconvenient and unsatisfactory to discuss detached portions of the subject with casual objectors, the more so, as objections are too often raised, not with the view of searching after truth, and aiding in the inquiry, by throwing additional light on the subject, but merely for the sake of opposition. Where also such controversy is carried on, manifestly under personal, rather than scientific notions, it can lead to nothing useful, and therefore I beg to decline it; reasserting that as the subject is one of great interest, I shall at all times be glad to be set right where I may state chemical facts erroneously, or draw inaccurate inferences,

I am, Sir, yours, &c.,

Liverpool, March 14, 1841.

C. W. WILLIAMS.

ON THE CAUSES OF FIRE-DANGER OF DISCARDED CONGREVE-MATCHES, OPEN CANDLES, ETC.

Sir,-Too much stress cannot be laid upon the remark of Mr. Booth, quoted in my last, (page 175,) "that by atten tion to the published causes of fire, great good will be accomplished;" and I would wish to make a few observations on the immense danger to which he has advert ed, of a careless or thoughtless use of congreve matches, now in such universal employment for the production of light. Many persons know by painful experience the consequences of kindling one of these matches immediately over, or in close contiguity to a quantity; beyond the per