essays-1-第55节
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I have hitherto given no precise directions in regard to the height to which the new back and covings ought to be carried： This will depend not only on the height of the mantle； but also； and more especially； on the height of the breast of the Chimney； or of that part of the Chimney where the breast ends and the upright canal begins。The back and covings must rise a few inches； five or six for instance； higher than this part； otherwise the throat of the Chimney will not be properly formed：but I know of no advantages that would be gained by carrying them up still higher。
I mentioned above； that the space between the walls which form the new back and covings； and the old back and sides of the Fire…place； should be filled up：but this must not be understood to apply to the space between the wall of dry bricks； or the tile which closes the passage for the Chimney…sweeper； and the old back of the Chimney； for that space must be left void； otherwise； though this tile （which at most will not be more than two inches in thickness；） were taken away； there would not be any room sufficient for him to pass。
In forming this door…way； the best method of proceeding is to place the tile or flat piece of stone destined for closing it； in its proper place； and to build round it； or rather by the sides of it； taking care not to bring any mortar near it； in order that it may be easily removed when the door…way is finished。With regard to the rabbet which should be made in the door…way to receive it and fix it more firmly in its place； this may either be formed at the same time when the door…way is built； or it may be made after it is finished； by attaching to its bottom and sides； with strong mortar； pieces of thin roof tiles。 Such as are about half an inch in thickness will be best for this use； if they are thicker； they will diminish too much the opening of the door…way； and will likewise be more liable to be torn away by the Chimney…sweeper in passing up and down the Chimney。
It will hardly be necessary for me to add； that the tile； or flat stone； or wall of dry bricks； which is used for closing up the door…way； must be of sufficient height to reach quite up to a level with the top of the walls which form the new back and covings of the Chimnies。
I ought； perhaps； to apologize for having been so very particular in these description and explanations； but it must be remembered that this chapter is written principally for the information of those who； having had few opportunities of employing their attention in abstruse philosophical researches； are not sufficiently practised in these intricate investigations； to seize； with facility； new ideas；and consequently； that I have frequently been obliged TO LABOUR to make myself understood。
I have only to express my wishes that my reader may not be more FATIGUED with this labour than I have been；for we shall them most certainly be satisfied with each other。But to return once more to the charge。
There is one important circumstance respecting Chimney Fire…places； destined for burning coals； which still remains to be farther examined；and that is the Grate。
Although there are few grates that may not be used in Chimneys constructed or altered upon the principles here recommended； yet they are not； by any means； all equally well adapted for that purpose。Those whose construction is the most simple； and which of course are the cheapest； are beyond comparison the best； ON ALL ACCOUNTS。Nothing being wanted in these Chimnies but merely a grate for containing the coals； and in which they will burn with a clear fire；and all additional apparatus being； not only useless； but very pernicious； all complicated and expensive grates should be laid aside； and such as more simple substituted in the room of them。And in the choice of a grate； as in every thing else； BEAUTY and ELEGANCE may easily be united with the MOST PERFECT SIMPLICITY。Indeed they are incompatible with every thing else。
In placing the grate； the thing principally to be attended to is； to make the back of it coincide with the back of the Fire…place； but as many of the grates now in common use will be found to be too large； when the Fire…places are altered and improved； it will be necessary to diminish their capacities by filling them up at the back and the sides with pieces of fire…stone。 When this is done； it is the front of the flat piece of fire…stone which is made to form a new back to the grate； which must be made to coincide with； and make part of the back； of the Fire…place。 But in diminishing the capacities of grates with pieces of fire…stone； care must be taken not to make them TOO NARROW。
The proper width for grates destined for rooms of a middling size will be from six to eight inches； and their length may be diminished more or less； according as the room is heated with more or less difficulty； or as the weather is more or less severe。 But where the width of a grate is not more than five inches； it will be very difficult to prevent the fire from going out。
It goes out for the same reason that a live coal from the grate that falls upon the hearth soon ceases to be red hot；it is cooled by the surrounding cold air of the atmosphere。 The knowledge of the cause which produces this effect is important； as it indicates the means which may be used for preventing it。 But of this subject I shall treat more fully hereafter。
It frequently happens that the iron backs of grates are not vertical； or upright； but inclined backwards。When these grates are so much too wide as to render it necessary to fill them up behind with fire…stone； the inclination of the back will be of little consequence； for by making the piece of stone with which the width of the grate is to be diminished in the form of a wedge； or thicker above than below； the front of this stone； which in effect will become the back of the grate； may be made perfectly vertical； and the iron back of the grate being hid in the solid work of the back of the Fire…place； will produce no effect whatever； but if the grate be already so narrow as not to admit of any diminution of its width； in that case it will be best to take away the iron back of the grate entirely； and fixing the grate firmly in the brick…work； cause the back of the Fire…place to serve as a back to the grate。This I have very frequently done； and have always found it to answer perfectly well。
Where it is necessary that the fire in a grate should be very small； it will be best； in reducing the grate with fire…stone； to bring its cavity； destined for containing the fuel； to the form of one half of a hollow hemisphere； the two semicircular openings being one above； to receive the coals； and the other in front； or towards the bars of the grate； for when the coals are burnt in such a confined space； and surrounded on all sides； except in the front and above； by fire…stone； （a substance peculiarly well adapted for confining heat；） the heat of the fire will be concentrated； and the cold air of the atmosphere being kept at a distance； a much smaller quantity of coals will burn； than could possibly be made to burn in a grate where they would be more exposed to be cooled by the surrounding air； or to have their heat carried off by being in contact with iron； or with any other substance through which heat passes with greater facility than through fire…stone。
Being persuaded that if the improvements in Chimney Fire…places here recommended should be generally adopted； （which I cannot help flattering myself will be the case；） that it will become necessary to reduce； very considerably； the sizes of grates； I was desirous of showing how this may； with the greatest safety and facility； be done。
Where grates； which are designed for rooms of a middling size； are longer than 14 or 15 inches； it will always be best； not merely to diminish their lengths； by filling them up at their two ends with fire…stone； but； forming the back of the Chimney of a proper width； without paying any regard to the length of the grate； to carry the covings through the two ends of the grate in such a manner as to conceal them； or at least to conceal the back corners of them in the walls of the covings。
I cannot help flattering myself that the directions here given in regard to the alterations which it may be necessary to make in Fire…places； in order to introduce the improvements proposed； will be found to be so perfectly plain and intelligible that no one who reads them will be at any loss respecting the manner in which the work is to be performed； but as order and arrangement tend much to facilitate all mechanical operations； I shall here give a few short directions respecting the manner of LAYING OUT THE WORK； which may be found useful； and particularly to gentlemen who may undertake to be their own architects； in ordering and directing the alterations to be made for the improvement of their Fire…places。
Directions for laying out the Work。
If there be a grate in the Chimney which is to be altered； it will always be best to take it away； and when this is done； the rubbish must be removed； and the hearth swept perfectly clean。
Suppose the annexed figure No。 1。 to represent the ground plan of such a Fire…place； A B being the opening
