380 S. Webber on Ventilation. 
passed through the lungs, then it would appear that the lower 
part of the room occupied by the oxygen united in the lungs 
with carbon might well be said to be occupied with spent air. 
Any nitrogen or carbonic acid in excess in the air may alike 
be looked upon as impurities. But even in impurity there 
may be a choice of kinds, and the question arises, is it so in this 
case? ‘This is easily answered, nitrogen is only negatively suf- 
focating,—carbonic acid is positively poisonous. It is therefore 
more iniportant to withdraw from an inhabited room the carbonie 
acid, and of consequence more important to have the ventilating 
aperture, if there be but one, near the floor, than near the ceiling ; 
and if the preservation of warmth in the room be an object, this 
is also best promoted by the samearrangements. Another open- 
ing near the ceiling will also be advantageons, but it must be 
arranged with a view to as little escape of warmth as may be 
consistent with reasonable preservation of the purity of the air, 
at least when the retention of warmth is desirable. Si 
a close room be inhabited, carbonic acid is not the only im-_ 
purity communicated to the air; there are frequently thrown off 
from the human body small portions of sulphuretted hydrogen 
and ammoniacal vapor, &c., which are as unfit for breathing ot 
closed windows, when the season will not admit of their. being 
. . ré 
imperative in proportion to the number of persons present for 
any time in the room; buat with doors and windows sufficiently 
tilation, and render the need of it less felt, when the persons in 
the room are but few in proportion to its size, ' 
The more closely the doors aud windows fit, the more large 
must be the veutilating openings, or instead of making them 
larger, artificial means of creating a current of air. t them 
must be employed. 
