Fig. 7, 8, and 9, show a plan, elevation, and section of a Fire-place constructed or altered upon this principal.--The wall of the Chimney in front at a, fig. 9, being only four inches thick, four inches more added to it for the width of the throat would have left the depth of the Fire-place measured upon the hearth b c only eight inches, which would have been too little;--a niche c and e, was therefore made in the new back of the Fire-place for receiving the grate, which niche was six inches deep in the center of it, below 13 inches wide, (or equal in width to the grate,) and 23 inches high; finishing above with a semicirular arch, which, in its highest part, rose seven inches above the upper part of the grate.--The door-way for the Chimney-sweeper, which begins just above the top of the niche, may be seen distinctly in both the figures 8 and 9.--The space marked g, fig. 9, behind this door-way, may either be filled with loose bricks, or may be left void.--The manner in which the piece of stone f, fig. 9, which is put under the mantle of the Chimney to reduce the height of the opening of the Fire-place, is rounded off on the inside in order to give a fair run to the column of smoke in its ascent through the throat of the Chimney, is clearly expressed in this figure. The plan fig. 7, and elevation fig. 8, show how much the width of the opening of the Fire-place in front is diminished, and how the covings in the new Fire-place are formed. A perfect idea of the form and dimension of the Fire-place in its original state, as also after its alteration, may be had by careful inspection of these figures. I have added the drawing fig. 10, merely to show how a fault, which I have found workmen in general whom I have employed in altering Fire-places are very apt to commit, is to be avoided. --In Chimneys like that represented in this figure, where the jambs A and B project far into the room, and where the front edge of the marble slab, o which forms the coving, does not come so far forward as the front of the jambs, the workmen in constructing the new covings are very apt to place them,--not in the line c A, which they ought to do,--but in the line c o, which is a great fault.--The covings of a Chimney should never range BEHIND the front of the jambs, however those jambs may project into the room;--but it is not absolutely necessary that the covings should MAKE A FINISH with the internal front corners of the jambs, or that they should be continues from the back c, quite to the front of the jambs at A.--They may finish in front at a and b, and small corners A, o, a, may be left for placing the shovels, tongs, etc. Were the new coving to range with the front edge of the old coving o, the obliquity of the new coving would commonly be too great;--or the angle d c o would exceed 135 degrees, WHICH IT NEVER SHOULD DO,--or at least never by more than a very few degrees.