S. Webber on Ventilation. 183 
the jambs, which openings may be more or less, or wholly closed 
at. pleasure, by some contrivance like a sliding lid or valve. In. 
this case the air for the support of the fire will be furnished from . 
the lower part of the room, and consists of the coldest part of 
the air in the room, and that most contaminated with carbonic 
acid gas. This by the constant ascent of the warm air from the 
supply openings to the upper part of the room, will be constantly 
and equably pressed towards the only mode of escape for it, the 
opening of the fire-place into the chimney above, and it will at 
the same time be drawn thither by the suction occasioned by the 
rarefaction and_ascent of the air in the chimney from the action 
of the fire. The air of the room will thus be perpetually renew- 
ed, and the renewal will be made with warm pure airs. Unless 
the room be over crowded, over lighted, or over heated, no other 
may be built in the common way of brick, the only objection being, 
that this material is a slow conductor of heat, aud considerable time 
must elapse after the kindling of the fire, before any perceptible 
fect can be noticed on the air contained in the hollows. Brick 
hioreover, in houses of the better class, will hardly be considered 
handsome enough. A fire-place constructed of slabs of soapstone 
Will be better in both of these points, though it is by no means 
80 good a conductor of heat as iron, while it is a better one than 
rick. It may however be observed that by way of compensar 
tion, though the air in the hollows will not be warmed so quickly 
by these two substances, yet that it will continue to be wa 
longer after the fire has gone out; as they seem to have a much 
Steater capacity for caloric than iron, aud under equal circumstan- 
%es will continue to impart it long after iron has become co 
‘be porcelain of which stoves are frequently constructed in 
sie economy of fuel the upper part 
Place he id be brought forward, so as to leave the throat of the 
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