S. Webber on Ventilation. 185 
unexceptionable, or even not in a considerable degree otherwise, 
is very doubtful to say the least. As generally constructed, the 
part of the furnace containing the fire and through which the 
caloric passes to be communicated to the air admitted between 
the inner and outer walls, is made of iron, and as the fire within 
is large and often fierce, it must, when much warmth is required, 
be often very intensely heated, so as not only to decompose the 
air, as before stated, but even the watery vapor contained in it, 
and thus throw into the rooms not only air with an undue por- 
tion of nitrogen, but unduly dry, and still more unfit for breath- 
ing from being contaminated with hydrogen. Furthermore, 
when there is, as is almost always the case, any fine organic dust 
floating in the atmosphere, such of this as comes in contact with 
the iron, if that-should be at a red heat, will in part at least be 
with the flue of a chimney, or with an up-draught pipe. 
pen stoves, as they are called, are but modifications of fire- 
cart by a pipe leading from the external air beneath the floor. 
This air, mr me by passing through seg oo et ie * 
back i itted to pass through a register 1 
and sides, may be permitt gee ae Gitavdie wave: 
