up the new back of the
fire-place, when this wall is brought up so high that there remains no
more than about ten or eleven inches between what is then the top of it
and the underside of the mantle, an opening or door-way, eleven or
twelve inches wide, must be begun in the middle of the back, and
continued quite to the top of it, which according to the height that it
will commonly be necessary to carry up the back, will make the opening
twelve or fourteen inches high, which will be quite sufficient for the
purpose. When the fire-place is finished, this door-way is to be closed
by a few bricks laid without mortar, or a tile or piece of stone
confined in its place by means of a rebate made for that purpose in the
brick-work. As often as the chimney is swept, the chimney sweeper
removes this temporary wall or stone, which is very easily done, and
when he has finished his work, he again puts it in its place. The new
back and covings may be built either of brick-work or of stone, and the
space between them and the old back and covings, ought to be filled up
to give greater solidity to the structure. This may be done with loose
rubbish or pieces of broken bricks or stones, provided the work be
strengthened by a few layers or courses of bricks laid in mortar; but it
will be indispensably necessary to finish the work where these new walls
end, that is to say, at the top of the throat of the chimney, where it
ends abruptly in the open canal or flue, by a horizontal course of
bricks well secured with mortar. It is of much importance that they
should terminate in this manner; for were they to be sloped outward and
raised in such a manner as to swell out the upper extremity of the
throat of the chimney in the form of a trumpet, and increase it by
degrees to the size of the flue of the chimney, this construction would
tend to assist the winds which may attempt to blow down the chimney, in
forcing their way through the throat, and throwing the smoke backward
into the room. The internal form of the breast of the chimney is also a
matter of great importance, and which ought to be particularly attended
to. The worst form it can have is that of a vertical plane or upright
flat, and next to this the worst form is an inclined plane. Both these
forms cause the current of warm air from the room which will, in spite
of every precaution, sometimes find its way into the chimney, to cross
upon the current of smoke which rises from the fire in a ma