. The Ontario public school hygiene . resh air comes inat the bottom. The objection to this is that thosewho are near the window may catch cold from sittingin a draught. Figure 2.—Air mov-ing- upwards froma lighted lamp. VENTILATION 19 ..^stuffy uif oat A much better way is to make the stuffy air leave aroom through an outlet tube or duct which lies close tothe chimney. When an outlettube is close to a warm chim-ney, the chimney will heat theair in the tube and will thusmake it lighter, causing it toascend in the tube and so passout at the top of the roof. This outlet duct should openfrom a ro
. The Ontario public school hygiene . resh air comes inat the bottom. The objection to this is that thosewho are near the window may catch cold from sittingin a draught. Figure 2.—Air mov-ing- upwards froma lighted lamp. VENTILATION 19 ..^stuffy uif oat A much better way is to make the stuffy air leave aroom through an outlet tube or duct which lies close tothe chimney. When an outlettube is close to a warm chim-ney, the chimney will heat theair in the tube and will thusmake it lighter, causing it toascend in the tube and so passout at the top of the roof. This outlet duct should openfrom a room at two places—near the floor, and also nearthe ceiling, because expiredair being heavier than freshair tends to fall to the floor,especially when both kinds of air are of the same tem-perature. Tf then there is only one outlet duct near theceiling, the foul air can not escape and must thereforeaccumulate along the floor. That foul air does accumulate in this way can easilybe proved by placing a candle on the floor of a crowded. Figure 3.—Slantiri)^ board, arranged sothat it can be adjusted to deflect theincoming draft upward. The uppersash lowered, the lower sash raised. Q room in which there is little or no the course of an hour or so the candle willgrow dimmer and dimmer, and finally go will not go out at all, or at least not soquickly, if placed higher up in the room. Thefollowing experiment also illustrates this fact:— Fit a cork into the lower end of a tall lamp-chimney so tightly that no air can enter aroundit. Now remove the cork temporarily and place uponit a short piece of a lighted candle. Insert the corkagain and watch what happens. The caudle will soon FlQURB 4. 20 PUBLIC SCHOOL HYGIENE go out,—and for precisely the same reason as it willgo out when placed upon the floor of an unventilatedroom. (Fig. 4.) As the stuffy air escapes from a room, fresh aircomes in through walls and chinks wherever it can find entrance. Of course thequa
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