Page:Popular Science Monthly Volume 11.djvu/225

Rh and crevices is of greater influence than large communications with the outer air at a small difference of temperature.

The roaring fire and the draught of the stove produced only an increase of 700 cubic feet—one-third only of the necessary ventilation per head. I have examined a number of stoves opening into the room for the quantity of air which they abstract while the fire burns. The anemometer showed that it was never more than 3,105 cubic feet. Large wards in hospitals, schools, etc., heated by one open fireplace or stove, are sometimes wrongly believed to be well ventilated, because one perceives the air rushing into the same. But the main point is to know the quantity of required air and the quantity of outgoing air.

The free wall of a room of mine has been examined for its ventilating power. The room contained 2,650 cubic feet, and at 9.5° Fahr. difference of temperature between outside and inside, the spontaneous ventilation through each square yard amounted to about seven cubic feet, or forty-three gallons per hour.

Mãrker and Schultze, in their researches on the spontaneous ventilation of stables, have found for one square yard of a free wall, at 9.5° Fahr. difference of temperature, that the spontaneous ventilation amounted per hour—

Domestic animals, according to Mãrker, require a proportionately smaller change of the air than man. Stable-air may contain up to three per mil. carbonic acid. While man's ventilation requires 2,100 cubic feet per hour, 1,050 are sufficient for full-grown cattle, although their bodies and consumption of air are so much larger. The ventilation of stables depends chiefly on the size and porosity of their free walls. It has been found that the 1,050 cubic feet mentioned above were furnished by—

A stable built up of mud can therefore shelter many more animals than one built of sandstone, etc. "As the strength of the natural ventilation of a stable does not depend on the cubic space of the stable, but on the extent of its ventilating walls, it follows that in a small stable a proportionately greater ventilation takes place than in a greater one, because for each animal there is more ventilating surface with equal cubic space."