Here p = ·0004. P = ·6 × 6 × 4 = 14·4. A = 2,000 × 6 × 4 + 3,000 = 51,000. x = ·004 + 14·4∕51,000 = ·000682 = 6·82 parts CO₂ in 10,000 of air. _The air of a room occupied by 6 persons and containing 5,000 cubic feet of space, yields 7·5 parts of CO₂ per 10,000 parts of air. How much air is being supplied per hour?_ A = P/(x - p) = ·6 x 6/(·00075 - ·0004) = +10,280+ cubic feet. _In the same room what would be the condition of the air at the end of 4 hours?_ x = ·0001 + ·6 × 6 × 4/(10280 × 4 + 5,000) = ·0004 + 14·4∕46,120 = ·000712 = +7·12 of CO₂+ in 10,000 of air. _Given two sleeping rooms, Y 10 ft. by 15 ft. and 10 ft. high, Z 15 ft. by 20 ft. and 12 ft. high, with three adults in each; how much fresh air would you supply in each? What would be the condition of the air of each of the rooms after, 1∕4, 1∕2, 1, and 2 hours respectively?_ Amount of fresh air to be supplied in _Y_— A = P/(x - p) = ·6 × 3/(·0005 - ·0004) = _9,000_ cubic feet per hour. Condition of air in Y after 1∕4 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— P = ·6 × 4 = 2·4. A = 2,000 × 4 + 1,000 = 9,000. p = ·0004. x = ·0004 + 2·4∕9,000 = +·000667+. 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.