Condition of air in Y after ¼ hour—

Here p = ·0004.
P = ·6 × 3  ∕  4= ·45.
A = 9,000  ∕  4 + 1,500 = 3,750.
x = ·0004 + ·45  ∕  3,750 = ·00052.

At the end of 2 hours—
x = ·0004 + 3·6∕(18,000 + 1,500) = ·000584.

And similarly for Z.

Suppose two rooms, one 10 feet cube, the other 50 feet by 20 feet and 15 feet high, have continuously admitted into each of them a volume of fresh air containing ·04 parts carbonic acid per 100 parts, amounting to 2,000 cubic feet per hour, so as to replace to that extent the air of the room; suppose also that an average adult be placed in each room: show by detailed calculation what would be the condition of impurity of air in each room, as measured by carbonic acid, at the end of 4 hours and 12 hours respectively.

In the case of the first room—

The amount of impurity at the end of 12 hours, and in the second room may be similarly ascertained.

Ventilation in relation to Temperature.—The temperature of a given atmosphere is a most important factor in determining the ease with which it is replenished from the external air. Speaking generally, the greater the difference between the temperature of two masses of air the more rapidly an interchange occurs.

Air has weight. A column of it one inch square and extending to the uppermost limit of the atmosphere weighs about 14·6 lbs., and exerts this pressure on all substances at the surface of the earth. This pressure is exerted uniformly in all directions; but for this fact our chests would be crushed in by the external pressure on them, which amounts to over four tons. If the atmospheric pressure is diminished at any point, it is evident that the surrounding air will tend to press in this direction. Now, when air is heated it expands, and consequently the heavier fresh air flows in from all sides and pushes the lighter air upwards.