e…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 of it in front； A C and B D the two sides or covings； and C D the back。
Figure 2。 shows the elevation of this Fire…place。
First draw a strait line； with chalk； or with a lead pencil； upon the hearth； from one jamb to the other；even with the front of the jambs。 The dotted line A B； figure 3； may represent this line。
From the middle C of this line； （A B） another line c d； is to be drawn perpendicular to it； across the hearth； to the middle d； of the back of the Chimney。
A person must now stand upright in the Chimney； with his back to the back of the Chimney； and hold a plumb…line to the middle of the upper part of the breast of the Chimney （d； fig。 5；） or where the canal of the Chimney begins to rise perpendicularly； taking care to place the line above in such a manner that the plumb may fall on the line c d； draw on the hearth from the middle of the opening of the Chimney in front to the middle of the back； and an assistant must mark the precise place e； on that line where the plumb falls。
This being done； and the person in the Chimney having quitted his station； four inches are to be set off the line c d； from e； towards d； and the point f； where these four inches end； （which must be marked with chalk； or with a pencil；） will show how far the new back is to be brought forward。
Through f； draw the line g h； parallel to the line A B； and this line g h will show the direction of the new back； or the ground line upon which it is to be built。
The line c f will show the depth of the new Fire…place； and if it should happen that c f is equal to about ONE…THIRD of the line A B； and if the grate can be accommodated to the Fire…place instead of its being necessary to accommodate the Fire…place to the grate； in that case； half the length of the line c f； is to be set off from f on the line g f h； on one side to k； and on the other to i； and the line i k will show the ground line of the fore part of the back of the Chimney。
In all cases where the width of the opening of the Fire…place in front （A B） happens to be not greater； or not more than two or three inches greater than THREE TIMES the width of the new back of the Chimney （i k）； this opening may be left； and lines drawn from i to A； and from k to B； will show the width and position of the front of the new covings；but when the opening of the Fire…place in front is still wider； it must be reduced； which is to be done in the following manner：
From c； the middle of the line A B； c a and c b； must be set off equal to the width of the back （i k）； added to half its width （f i）； and lines drawn from i to a； and from k to b； will show the ground plan of the fronts of the new covings。
When this is done； nothing more will be necessary than to build up the back and covings； and if the Fire…place is designed for burning coals； to fix the grate in its proper place； according to the directions already given。When the width of the Fire…place is reduced； the edges of the covings a A and b B are to make a finish with the front of the jambs。And in general it will be best； not only for the sake of the appearance of the Chimney； but for other reasons also； to lower the height of the opening of the Fire…place； whenever its width in front is diminished。
Fig。 4。 shows a front view of the Chimney after it has been altered according to the directions here given。By comparing it with fig。 2。 （which shows a front view of the same Chimney before it was altered）； the manner in which the opening of the Fire…place in front is diminished may be seen。In fig。 4。 the under part of the door…way by which the Chimney…sweeper gets up the Chimney is represented by white dotted lines。 The door…way is represented closed。
I shall finish this chapter with some general observations relative to the subject under consideration； with directions how to proceed where such local circumstances exist as render modifications of the general plan indispensably necessary。
Whether a Chimney be designed for burning wood upon the hearth； or wood； or coals in a grate； the form of the Fire…place is in my opinion； most perfect when THE WIDTH OF THE BACK is equal to the DEPTH OF THE FIRE…PLACE； and the opening of the Fire…place in front equal to THREE TIMES the width of the back； or； which is the same thing； to THREE TIMES THE DEPTH OF THE FIRE…PLACE。
But if the Chimney be designed for burning wood upon the hearth； upon hand irons； or dogs； as they are called； it will sometimes be necessary to accommodate the width of the back to the length of the wood； and when this is the case； the covings must be accommodated to the width of the back； and the opening of the Chimney in front。
When the wall of the Chimney in front； measured from the upper part of the breast of the Chimney to the front of the mantle； is very thin； it may happen； and especially in Chimnies designed for burning wood upon the hearth； or upon dogs； that the depth of the Chimney； determined according to the directions here given； may be too small。
Thus； for example； supposing the wall of the Chimney in front； from the upper part of the breast of the C