essays-1-第57章
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cing of the throat of a Chimney VERY NEAR the burning fuel。 In introducing the improvements proposed； in Chimnies already built； there can be no question in regard to the height of the throat of the Chimney； for its place will be determined by the height of the mantle。 It can hardly be made lower than the mantle； and it ought always to be brought down as nearly upon the level with the bottom of it as possible。 If the Chimney is apt to smoke； it will sometimes be necessary either to lower the mantle or to diminish the height of the opening of the Fire…place； by throwing over a flat arch； or putting in a straight piece of stone from one side of it to the other； or； which will be still more simple and easy in practice； building a wall of bricks； supported by a flat bar of iron； immediately under the mantle。
Nothing is so effectual to prevent Chimnies from smoking as diminishing the opening of the Fire…place in the manner here described； and lowering and diminishing the throat of the Chimney； and I have always found； except in the single instance already mentioned； that a perfect cure may be effected by THESE MEANS ALONE； even in the most desperate cases。 It is true； that when the construction of the Chimney is very bad indeed； or its situation very unfavourable to the ascent of the smoke； and especially when both these disadvantages exist at the same time； it may sometimes be necessary to diminish the opening of the Fire…place； and particularly to lower it； and also to lower the throat of the Chimney； more than might be wished： but still I think this can produce no inconveniences to be compared with that greatest of all plagues； a smoking Chimney。
The position of the throat of a Chimney being determined； the next points to be ascertained are its size and form； and the manner in which it ought to be connected with the Fire…place below； and with the open canal of the Chimney above。
But as these investigations are intimately connected with those which relate to the form proper to be given to the Fire…place itself； we must consider them all together。
That these inquiries may be pursued with due method； and that the conclusions drawn from them may be clear and satisfactory； it will be necessary to consider； first； what the objects are which ought principally to be had in view in the construction of a Fire…place； and secondly； to see how these objects can best be attained。
Now the design of a Chimney Fire being simply to warm a room； it is necessary； first of all； to contrive matters so that the room shall be actually warmed； secondly； that it be warmed with the smallest expence of fuel possible； and； thirdly； that in warming it； the air of the room be preserved perfectly pure； and fit for respiration； and free from smoke and all disagreeable smells。
In order to take measures with certainty for warming a room by means of an open Chimney Fire； it will be necessary to consider HOW； or in WHAT MANNER； such a Fire communicates heat to a room。 This question may perhaps； at the first view of it； appear to be superfluous and trifling； but a more careful examination of the matter will show it to be highly deserving of the most attentive investigation。
To determine in what manner a room is heated by an open Chimney Fire； it will be necessary first of all to find out； UNDER WHAT FORM the heat generated in the combustion of the fuel exists； and then to see how it is communicated to those bodies which are heated by it。
In regard to the first of these subjects of inquiry； it is quite certain that the heat which is generated in the combustion of the fuel exists under TWO perfectly distinct and very different forms。 One part of it is COMBINED with the smoke； vapour； and heated air which rise from the burning fuel； and goes off with them into the upper regions of the atmosphere； while the other part； which appears to be UNCOMBINED； or； as some ingenious philosophers have supposed； combined only with light； is sent off from the fire in rays in all possible directions。
With respect to the second subject of inquiry； namely； how this heat； existing under these two different forms； is communicated to other bodies； it is highly probable that the combined heat can only be communicated to other bodies by ACTUAL CONTACT with the body with which it is combined； and with regard to the rays which are sent off by burning fuel； it is certain that THEY communicate or generate heat only WHEN and WHERE they are stopped or absorbed。 In passing through air； which is transparent； they certainly do not communicate any heat to it； and it seems highly probable that they do not communicate heat to solid bodies by which they are reflected。
In these respects they seem to bear a great resemblance to the solar rays。 But in order not to distract the attention of my reader； or carry him too far away from the subject more immediately under consideration； I must not enter too deeply into these inquiries respecting the nature and properties of what has been called RADIANT HEAT。 It is certainly a most curious subject of philosophical investigation； but more time would be required to do it justice than we now have to spare。 We must therefore content ourselves with such a partial examination of it as will be sufficient for our present purpose。
A question which naturally presents itself here is。 What proportion does the radiant heat bear to the combined heat？Though that point has not yet been determined with any considerable degree of precision； it is； however； quite certain； that the quantity of heat which goes off combined with the smoke； vapour； and heated air is much more considerable； perhaps three of four times greater at least； than that which is sent off from the fire in rays。And yet； small as the quantity is of this radiant heat； it is the only part of the heat generated in the combustion of fuel burnt in an open Fire…place which is ever employed； or which can ever be employed； in heating a room。
The whole of the combined heat escapes by the Chimney； and is totally lost； and； indeed； no part of it could ever be brought into a room from an open Fire…place； without bringing along with it the smoke with which it is combined； which； of course； would render it impossible for the room to be inhabited。 There is； however； one method by which combining heat； and even that which arises from an open Fire…place； may be made to assist in warming a room； and that is by making it pass through something analogous to a German stove； placed in the Chimney above the fire。But of this contrivance I shall take occasion to treat more fully hereafter； in the mean time I shall continue to investigate the properties of open Chimney Fire…places； constructed upon the most simple principles； such as are now in common use； and shall endeavour to point out and explain all those improvements of which THEY appear to me to be capable。 When fuel is burnt in Fire…places upon this simple construction； where the smoke escapes immediately by the open canal of the Chimney； it is quite evident that all the combined heat must of necessity be lost； and as it is the radiant heat alone which can be employed in heating a room； it becomes an object of much importance to determine how the greatest quantity of it may be generated in the combustion of the fuel； and how the greatest proportion possible of that generated may be brought into the room。
Now the quantity of radiant heat generated in the combustion of a given quantity of any kind of fuel depends very much upon the management of the fire； or upon the manner in which the fuel is consumed。 When the fire burns bright； much radiant heat will be sent off from it； but when it is SMOTHERED UP； very little will be generated； and indeed very little combined heat； that can be employed to any useful purpose： most of the heat produced will be immediately EXPENDED in giving elasticity to a thick dense vapour or smoke which will be seen rising from the fire； and the combustion being very incomplete； a great part of the inflammable matter of the fuel being merely rarefied and driven up the Chimney without being inflamed； the fuel will be wasted to little purpose。 And hence it appears of how much importance it is； whether it be considered with
